Critical Assessment of the Mineralogical Collections At

Home , Dundasite, Gaspeite, Kutnohorite, Minrecordite, Monohydrocalcite, Quintinite

Examensarbete vid Institutionen för geovetenskaper Degree Project at the Department of Earth Sciences ISSN 1650-6553 Nr 391

Critical Assessment of the Mineralogical Collections at Uppsala University using Raman Spectroscopy Kritisk studie av de mineralogiska samlingarna vid Uppsala universitet med hjälp av Ramanspektroskopi

Yuliya Zhuk

INSTITUTIONEN FÖR

GEOVETENSKAPER

DEPARTMENT OF EARTH SCIENCES

Examensarbete vid Institutionen för geovetenskaper Degree Project at the Department of Earth Sciences ISSN 1650-6553 Nr 391

Yuliya Zhuk

ISSN 1650-6553

Critical Assessment of the Mineralogical Collections at Uppsala University using Raman Spectroscopy Yuliya Zhuk

The technique of Raman spectroscopy was applied in order to identify and characterize the number of minerals in the mineralogical collection at the Department of Earth Sciences. The collection was broadened with five rare carbonates borrowed from the collection of the Swedish Museum of Natural History in Stockholm. In total, 66 specimens were examined. The characteristics of interest included possible presence and nature of defects and impurities, degree of crystallinity, residual stresses, possible treatment by natural heat sources (e.g. radionuclides) or chemicals (e.g. polishing agents), and fluorescence. Raman spectroscopy was chosen as examination method because of its distinctive advantage over traditional techniques – a non-destructive probing of pristine materials and minimum or no preparation. Besides, Raman spectroscopy performs very well in collecting the needed characteristics, in terms of its sensitivity, as well ability to probe miniature grains in a matrix with a high spatial resolution. A portable system was used to identify the presence of impurities and the fingerprint of the host rock in the majority of the examined carbonates. The rare carbonate burbankite showed distinct fluorescence bands, which likely can be explained by its complicated chemical composition. The Raman system was used for gemmological purposes and helped to identify the purity of the gems. Diamond and two rubies showed to be free from impurities, but red corundum showed a broad peak, which may represent traces of natural heat treatment, which in turn could be caused by regional metamorphism or even by a radiation source. Furthermore, the correlation between the signal intensity of the fluorites’ bands and the chemical composition of the minerals were studied. The experiment showed that blue fluorite fully misses the peak T2g while purple and grey fluorites showed a well- developed and easily recognizable peak at this location. Thus, it was discovered that the presence and intensity of this peak is directly dependent on the fluorite’s colour, i.e. on the host species, which are incorporated in the crystal structure, such as metals, rare earth elements (REE) or even organic substances. Moreover, residual tensile stress was identified in colourless quartz. The tensile stress was estimated to be in the interval between 0.23 and 1.0 GPa. The Raman system was used to identify different end-members of the garnet family. Raman spectroscopy showed to have high analytical power and helped to estimate the ratio between the end- members in eight garnet samples. In one case, fluorescence was linked to the presence of REEs in the structure of almandine. One sample of calcite showed to be incorrectly placed in the collection. This work will now form a solid foundation for the mineral characteristics handbook.

Keywords: Raman spectroscopy, gemmology, geology, mineralogy, Mineralogical Collection

Degree Project E1 in Earth Sciences, 1GV025, 30 credits Supervisor: Peter Lazor Department of Earth Sciences, Uppsala University, Villavägen 16, SE-752 36 Uppsala (www.geo.uu.se)

ISSN 1650-6553, Examensarbete vid Institutionen för geovetenskaper, No. 391, 2017

The whole document is available at www.diva-portal.org

Populärvetenskaplig sammanfattning

Kritisk studie av de mineralogiska samlingarna vid Uppsala universitet med hjälp av Ramanspektroskopi Yuliya Zhuk

Ramanspektroskopitekniken applicerades för att identifiera och karakterisera antalet mineraler i den mineralogiska samlingen vid Institutionen för geovetenskaper. Samlingen breddades med fem sällsynta karbonater som lånades från Naturhistoriska riksmuseets samling i Stockholm. Sammanlagt analyserades 66 prover. Egenskaperna av intresse inkluderade eventuell förekomst av och karaktären hos defekter och föroreningar, graden av kristallinitet, restspänningar, eventuella spår av naturlig värmebehandling (till exempel radionuklider) eller kemisk behandling (till exempel polermedel), och fluorescens. Ramanspektroskopi valdes som undersökningsmetod på grund av dess tydliga fördel över traditionella metoder – en icke-förstörande undersökning av rena material och minimal eller ingen förberedelse. Därutöver fungerar Ramanspektroskopi väldigt bra för undersökning av de efterfrågade egenskaperna, vad gäller dess känslighet och kapacitet vid sondering av miniatyrkorn i matriser med hög spatial upplösning. Ett portabelt system användes för att identifiera föroreningar och fingeravtryck av den omslutande bergarten i de flesta undersökta karbonatprov. Den sällsynta karbonaten burbankit visade på distinkta fluorescensband, som sannolikt kan tillskrivas dess komplicerade kemiska sammansättning. Ramansystemet användes i gemmologiskt syfte och kunde identifiera ädelstenarnas renhet. Diamant och två rubiner visade sig sakna föroreningar, men den röda korunden visade en bred topp, som kan indikera på spår av naturlig värmebehandling, som i sin tur kan ha orsakats av regional metamorfos eller till och med en strålningskälla. Därutöver studerades sambandet mellan signalstyrkan hos fluoriters band och mineralers kemiska sammansättning. Experimentet visade att blå fluorit fullständigt saknar toppen från T2g, medan de lila och grå fluoriterna hade välutvecklade och lättigenkännliga toppar vid denna position. Således upptäcktes att denna topps närvaro och intensitet är direkt beroende av fluroritens färg, det vill säga av elementen som är inkorporerade i kristallstrukturen, så som metaller, sällsynta jordartsmetaller eller till och med organiska substanser. Därutöver identifierades restdragspänning i den färglösa kvartsen. Spänningen uppskattades ligga i intervallet 0.23 – 1.0 GPa. Ramansystemet användes för att identifiera olika ändelement i granatfamiljen. Ramanspektroskopin hade hög analytisk förmåga och hjälpte till att estimera förhållandet mellan ändelementen i åtta granatprover. I ett fall kunde fluorescens bindas till förekomsten av sällsynta jordartsmetaller i almandinets struktur. Ett kalcitprov visade sig vara felaktigt placerat i samlingen. Detta arbete kommer nu utgöra en god grund för den mineralogiska samlingens handbok.

Nyckelord: Ramanspektroskopi, gemologi, geologi, mineralogi, mineralogisk samling

Examensarbete E1 i geovetenskap, 1GV025, 30 hp Handledare: Peter Lazor Institutionen för geovetenskaper, Uppsala Universitet, Villavägen 16, SE-752 36 Uppsala (www.geo.uu.se)

ISSN 1650-6553, Examensarbete vid Institutionen för geovetenskaper, Nr 391, 2017

Hela publikationen finns tillgänglig på www.diva-portal.org

Table of Contents

1 Introduction ...... 1

2 Objectives ...... 2

2.1 Scientific problems ...... 2

2.2 Testing hypotheses ...... 3

2.3 The broader value of the project ...... 4

3 Background ...... 4

3.1 Physics of Raman spectroscopy ...... 4

3.2 Interaction between the incitation source and the geomaterial...... 5

3.3 Common applications of Raman spectroscopy ...... 7

4 Methodology ...... 7

4.1 Materials ...... 7

4.2 Portable Raman spectrometer ...... 7

4.3 Experimental calibrations ...... 8

4.3.1 Calibration procedure ...... 9

4.4 PeakFit™ software ...... 11

4.5 Crystal Sleuth search engine ...... 12

5 Chapter I – Carbonates ...... 13

5.1 Background ...... 13

5.1.1 Anhydrous Carbonates ...... 16

5.1.2 Anhydrous Carbonates with Compound Formula A + B ++ (CO3)2 ...... 34

5.1.3 Anhydrous Carbonates with Compound Formula A+2 B++2 (CO3)4 ...... 37

5.1.4 Carbonates - Hydroxyl or Halogen (I) ...... 39 Table of Contents (cont.)

5.1.5 Carbonates - Hydroxyl or Halogen (II) ...... 42

5.2 Results ...... 45

5.2.1 Anhydrous Carbonates ...... 45

5.3 Discussion ...... 94

5.3.1 Anhydrous Carbonates ...... 94

5.3.1.2 Anhydrous Carbonates with Compound Formula A + B ++ (CO3 ...... 98

5.3.2 Carbonates - Hydroxyl or Halogen (I) ...... 99

5.4 Conclusions ...... 101

6 Chapter II – Applications of Raman spectroscopy to gemmology ...... 103

6.1 Background ...... 103

6.1.1 Precious gemstones ...... 103

6.1.2 Semi-precious gemstones ...... 107

6.2 Results ...... 118

6.2.1 Precious gemstone ...... 118

6.2.2 Semi-precious gemstones ...... 122

6.2.3 Fluorite ...... 133

6.3 Discussion ...... 145

6.3.1 Precious gemstone ...... 145

6.3.2 Semi-precious gemstones ...... 147

6.4 Conclusions ...... 150

7 Chapter III – Quartz family ...... 151

7.1 Background ...... 151 Table of Contents (cont.)

7.1.1 Pure colourless quartz ...... 152

7.1.2 Smoky quartz ...... 155

7.1.3 Amethyst ...... 156

7.1.4 Citrine ...... 159

7.1.5 Rose quartz ...... 160

7.1.6 Polishing agents ...... 162

7.2 Results ...... 162

7.2.1 Colourless transparent quartz ...... 162

7.2.2 Milky quartz ...... 164

7.2.3 Smoky quartz ...... 166

7.2.4 Amethyst ...... 171

7.2.5 Citrine ...... 175

7.2.6 Rose quartz ...... 180

7.3 Discussion and conclusions ...... 185

7.3.1 Pure and milky quartz ...... 185

7.3.2 Smoky quartz ...... 187

7.3.3 Amethyst and citrine ...... 187

7.3.4 Rose quartz ...... 188

8 Chapter IV – Garnet family ...... 188

8.1 Background ...... 188

8.1.1 Scientific background and what Raman spectroscopy can identify ...... 189

8.1.2 Raman spectroscopy of six main varieties of garnet ...... 191 Table of Contents (cont.)

8.2 Result ...... 202

8.2.1 Garnet 1 ...... 203

8.2.2 Garnet 2 ...... 204

8.2.3 Garnet 3 ...... 205

8.2.4 Garnet 4 ...... 207

8.2.5 Garnet 5 ...... 208

8.2.6 Garnet 6 ...... 209

8.2.7 Garnet 7 ...... 211

8.2.8 Garnet 8 ...... 212

8.3 Discussion ...... 213

8.4 Conclusions ...... 215

9 Final discussion and conclusions ...... 216

10 References ...... 217 1 Introduction

The mineralogical collection at the department of Earth Sciences at Uppsala university contains many minerals, used often both for teaching and research. Typically, several specimens of same mineral species of various morphology, texture, purity are available. In many cases, small grains/fragments of a mineral of interest are embedded in a bulk matrix. For mixed-mineral specimens, and for minerals of a similar appearance, the proper identification may represent a problem, not only for students but, in a case of dealing with some less common minerals, for researchers as well. Thus, from pedagogical and research points of view, it would be a great advantage if specimens in a collection are carefully examined by reliable analytical methods and the results of the examination are made available for users in the form of a handbook. Traditionally, the identification and even some properties/qualities of specimens have been assessed using simple methods in the classroom including, for example, hardness estimation, cleavage directions, reaction with an acid, magnetism etc (Wenk & Bulakh, 2012). A more advanced approach relies on application of techniques of polarized optical microscopy (in transmission and reflection configurations) on minerals prepared in a form of thin sections (Hawkes & Spence, 2007). Methods of x-ray diffraction and electron microprobe analysis have power to provide a further detailed mineral characterization but are too advanced, expensive and often not readily available. Application of the technique of Raman spectroscopy represents yet another approach to the characterization of minerals (Beran & Libowitzky, 2004). Its distinctive advantage over the traditional techniques is represented by a non-destructive probing of pristine materials, with a minimum or no preparation. By being able to address tasks of mineral identification, determination of crystal qualities/perfections, amount and nature of impurities, as well as to probe miniature grains in a matrix with a high spatial resolution, Raman spectroscopy represents a promising technique which can facilitate reaching objectives of the current project (Dubessy et al., 2012) Indeed, it may well turn out to be an ideal tool in terms of its relative simplicity, analytical power, cost, know-how and availability at the department. So far, a clear majority of analytical studies on minerals have been performed using stationary Raman systems located in research laboratories. Novelty in this project is that a portable system will be utilized. Such a system offers a greater flexibility when it comes to

1 choosing a convenient site the Raman analysis. More importantly, it allows probing exposed minerals and rocks directly in the field in their natural undisturbed setting.

2 Objectives

The project’s objectives include identification and characterization of minerals contained in the mineralogical collections for teaching and research at the Department of Earth Sciences, Uppsala University, and at the Museum of Natural History in Stockholm. As the above- mentioned collections are extensive, this study focuses on carbonates, gemmologically valuable minerals, quartzes and garnets.

2.1 Scientific problems The first scientific problem is mineral identification. More than 4000 minerals are known today. Identification of less common minerals may be a challenge. Moreover, as nature represents a largely open chemical system, it is not uncommon that seemingly nice specimens of nominally pure minerals contain small crystalline or fluid inclusions of other associated minerals/fluids (e.g. so called accessory minerals) whose identification, along with the main mineral, may provide important clues about the mineral’s origin (Dubessy et al., 2012; Prawer &Nemanich, 2004). Raman spectroscopy represents a convenient and powerful tool to address the issue of identification. Practically all minerals have been probed by Raman spectroscopy and their spectra are often freely available in spectral libraries (RRUFF; Mineral Raman Database (University of Parma); Raman Spectroscopic Library, UCL). The task of identification translates into finding a match between the acquired spectrum and spectrum from a library. Tiny solid or fluid inclusions can be selectively probed and identified by the Raman spectroscopy because of the high spatial resolution of this technique (ca 1 micron). The degree of matching and reliability of identification represent topics which require a proper scientific approach and background in that various factors, such as crystal orientations, presence of impurities/defects may partially mask the true vibrational signature of an unknown geomaterial (Beran & Libowitzky, 2004). As such, these topics represent a scientific problem to be tackled in their own right. Finding scientifically justified correlations/matches between the acquired spectra and those found in spectral libraries represents an important part of this project. The second scientific problem is mineral characterization. Clearly, there is more to the mineralogical assessment than the identification. A strong need exists to quantify impurities and crystal structure defects, stress-strain condition of the lattice, as these variables reflect 2 genesis of minerals, their geological history (e.g. subjection to metamorphic processes) (Effenberger et al., 1981; Korsakov et al., 2010; Spivak et al., 2014). In this case, the first step in solving the scientific task consists of a careful spectra analysis and peak-fitting (PeakFit, User’s Manual, 2003). As impurities/residual stresses will modify the interatomic distances and hence the strengths of bonds, the anomalously shifted peak positions will serve as markers of deviations from an ideally pure and stress-free crystal (Beran & Libowitzky, 2004). These imperfections also tend to enhance optical processes competing with the Raman scattering, most of all fluorescence. The fluorescence often results in appearance of broad background, which usually decreases the signal-to-noise ratio. Moreover, in some cases, new narrow spectral bands which are not predicted by the group-theoretical analysis appear and are mixed with the true Raman bands (Dubessy et al., 2012). These phenomena illustrate the scientific complexity of the Raman spectral analysis of impure minerals.

2.2 Testing hypotheses The critical spectroscopic assessment of minerals consists both in the evaluations of Raman spectra according to the established spectroscopic methodologies (determining peak widths and positions, nature of background, presence of fluorescence) (Beran & Libowitzky, 2004; (Dubessy et al., 2012) and in the comparison of the acquired spectra with those presented in on-line Raman databases (e.g. Rruff mineral database). The critical questions which are asked in this thesis, are exemplified by: Based on the acquired spectrum, is the mineral in the collection properly identified? Is the agreement/disagreement between the published and acquired spectra sufficient to be conclusive about the deviations from an ideal chemistry? Is a specimen pure mineral or a mixture of minerals? A hypothesis is tested each time when examining a mineral. When a reasonably close match with the spectral library is observed, further investigations on a given mineral – represented by collecting and evaluating multiple spectra collected from various spots, at different orientations – aim at testing the hypothesis that the mineral in the collection has been properly identified. The reasoning behind this approach is that minerals belonging to the same chemical/crystallographic group (e.g. carbonates, garnets) may exhibit quite similar spectra and a more detailed probing is required in order to reach a conclusive identity outcome (Buzgar & Apopei, 2009). In the next step, a detailed spectral analysis in the manner described above enables to test the hypothesis that the identified mineral is very pure.

2.3 The broader value of the project The output of the project, the thesis, will serve as a handbook of the mineralogical collection to be used by students, teachers and researchers. In addition to the Raman spectra and mineral assessments, the handbook will contain pictures of specimens in which locations of interest (spots, grains, crystals, crystal faces) will be identified.

3 Background

During the last few decades, Raman spectroscopy gained popularity among other methods in Earth Sciences, the main reason for such a success being an nondistructive and a simple application of this analytical method. Raman spectroscopy is based on the ability of atomic/molecular vibrations in a crystal to inelastically scatter photons. It is officially accepted that the Raman effect was discovered by Raman and Krishnan in 1928. However, Raman scattering, or the Raman effect, was predicted by Smekal already in 1923 and verified by the Russian scientists Landsberg and Mandelstam in 1928. Inelastic scattering implies that when a photon from the monochromatic light interacts with the target material, its frequency changes and shifts either up or down, compared to the original monochromatic frequency. The analysis of this shift can provide information about vibrational, rotational and other low type of motions motions in molecules (Beran & Libowitzky, 2004).

3.1 Physics of Raman spectroscopy The effect occurs when a sample is irradiated by an intense monochromatic light in the ultraviolet (UV) to infrared (IR) range, whereupon light is scattered elastically (Rayleigh) and inelastically (Raman). The inelastic scattering is much weaker than the incident light, so to be able to view the scattering, high-power lasers are needed (up to several hundreds of mW) and sensitive detectors are required. The laser light gets frequency-shifted depending on the vibrational modes of the target sample, hence, sample characteristics can be determined from the Raman spectrum. The Raman spectrum is symmetric in peak positions, but not symmetric in peak magnitudes. The peaks shifted to longer wavelengths are called Stokes, while the peaks shifted to shorter wavelengths are called anti- Stokes. The Stokes peaks are used for analysis most often, because they are normally stronger in amplitude and easier to record. Sometimes, however, the Stokes bands can be dominated by fluorescense; in this case, anti- Stokes provide more useful information. (Dubessy et al., 2012). A typical Raman stational measurement setup consists of the laser source, where its light is filtered and guided to a

4 sample via mirrors. The Rayleigh scattering is removed in the second (semi-transparent) mirror to make room for the weak Raman scattering. The gratings help to improve spectral resolution. Charge-coupled device (CCD) Detector is a silicon based multichannel one dimensional (linear) or two-dimensional (area) detector of UV, visible and near-infra light and consists of millions of detector elements (pixels). CCD is sensitive to light and, thus, is able to detect even weak Raman signals (Figure 1).

Figure 1. A typical Raman measurement setup. Source: Modified after Biswas et al., 2010.

3.2 Interaction between the incitation source and the geomaterial. When a sample, geomaterial, is irradiated with monochromatic light, photons are scattered inelastically and either lose (Stokes) or gain energy (Anti–Stokes). The emitted photons contain information about the molecular structure of the geomaterial. The elastically scattered photons have the same energy as the incident laser light (Rayleigh scattering). Modern Raman instruments are designed to filter out the Rayleigh light, leaving out just the Stokes or Anti- Stokes. Statistically there is only one in every million photons that will be Raman scattered. For a photon to be counted as Raman active, it should fulfil one important requirement – it should cause a change in polarizability of the molecules with which the photon interacted, i.e., a change in the shape, size or orientation of the electron cloud that surrounds the molecules of the sample (Beran & Libowitzky, 2004). The interaction with a Raman active photon provokes a vibrational excitation of a molecule. There are two different types of molecular motion: external and internal vibrations. External vibrations include translational motion and rotational motion. During external

5 vibration, the whole molecule is in motion. Internal vibration means that only some parts are in motion within the molecule. Internal vibration occurs when atoms in a molecule are in periodic motion, while the molecule as a whole has constant translational and rotational motion. The typical frequencies of molecule vibrations fall in the range of 1013 - 1014 Hz, corresponding to wavenumbers in the interval 300 - 3000 cm-1 (Dubessy et al., 2012). There are seven types of internal vibrations: stretching (symmetric and antisymmetric), bending or scissoring (symmetric and antisymmetric), rocking, wagging and twisting. If the symmetric and antisymmetric vibrations are counted as one, then there are five types of internal vibrations, as shown in Table 1. When thinking about the internal vibrations, it is helpful to define a plane, the “main plane”, that is defined by the centre atom and the two moving atoms. A vertical axis can be drawn, going through the centre atom and going between the two moving atoms. A horizontal axis can be drawn perpendicular to the vertical axis, in the “main plane”. Symmetric stretching occurs in the “main plane”, when the bond is elongated and shortened at the same time for both atoms. Antisymmetric stretching is the same type of bond vibration as symmetric stretching, but where the two moving atoms move in opposite directions along the bond axis. Bending is an oscillating change of the bond angle relative to the bonds. It occurs at a constant bond length and the two atoms move towards or against each other in sync. Rocking occurs when both the bond length and the angle between the bonds is kept constant, but when the atoms rock back and forth along the “main plane”. Wagging and twisting occurs when either of the two angles between the plane of the two atoms and the “main plane” oscillates. Wagging is an oscillating rotation around the horizontal axis, whereas twisting is an oscillating rotation around the vertical axis (Beran & Libowitzky, 2004).

Table 1. Different types of the internal vibrations and corresponding Greek symbols. Symbol Description

Ѵ Stretching (ѵs – symmetric; ѵas – antisymmetric

δ Bending / scissoring (δs – symmetric; δas – antisymmetric) ρ Rocking π, ω Wagging τ Twisting

3.3 Common applications of Raman spectroscopy

Raman spectroscopy is widely used in science. For example, it is used for spectroscopic analyses of gases, water and other geological fluids, for spectroscopy of silicate glasses and melts, for spectroscopy at high pressure and temperature for studying of Earth’s mantle and planetary minerals, in biogeology and astrobiology (e.g. in search for signatures of life on Mars), for spectroscopy of graphitic carbons in Earth Sciences, in gemmology, archaeology and solid state physics. (Dubessy et al., 2012; ESA, European Space Agency, 2016).

4 Methodology

4.1 Materials 66 minerals were studied in total: 25 carbonates, 17 gemstones, 16 quartz-samples and 8 garnets. 332 Raman spectra were taken and analysed. There were 5 Raman spectra taken per mineral, with the exception for burbankite because of its complex crystallographic structure, which required a more detailed study with 12 spectra. If a mineral exhibited recognizable crystal structure habit/morphology, the Raman spectra were taken along the c-axis, a-axis and at different angles to the c-axis. The results of the differences in the measurement were reported only if they were obvious. If there was no obvious difference in the measurements taken along a different axis, this detail was omitted. In the process of selecting minerals for the experiment, the main choice criteria were to find as differing minerals in the same group as possible. All measurements were taken by a portable Raman spectrometer. The measurement results were analysed by the PeakFit™ software and CrystalSleuth search engine. Before each new mineral experiment, the Raman system’s spectral axis was calibrated.

4.2 Portable Raman spectrometer Raman spectrometers are categorized by sensitivity and resolution. Sensitivity is characterized by the change of output per unit of input. Spectral resolution represents the smallest separation of two closely positioned bands at which these can still be spectrally resolved. Portable Raman spectrometers, such as the one used in this thesis, are in the mid-range of both sensitivity and resolution compared to the available lab equipment, and provide a good trade-off between ease-of-use and cost. The error estimation of confidence interval of measurements does not exceed 1 cm-1. The SLSR-ProTT Raman Analyzer from Enwave Optronics was used in this study. All parts are integrated into a case of ~46 cm x 36 cm x 19

7 cm. The vital parts are the laser and the analyzer. The laser comes from a frequency stabilized, narrow linewidth diode laser of class 3B with a maximum output power of 500mW and emitted wavelength of 785 nm. Class 3B is potentially hazardous if the eye is exposed by direct beam or specular reflections, and thus safety goggles have to be worn; diffused light from matte surfaces is not hazardous. Class 3B is the second-highest laser classification. Diode lasers differ from conventional lasers in several ways: they are much smaller making them highly portable, high efficiency allowing them to run on battery, low-intensity and with a wide-angle beam (Sun, 2012). The laser light is mediated by a flexible optical probe that can be pointed onto the sample. The scattered light is collected by a CCD detector and analyzed with the help of a spectrograph and a software on a laptop. CCD detector is also responsible for the acquisition of the data and presenting it on a graph with Raman shift on the spectral axis, between 0 and 2200 cm-1, and intensity on the vertical axis. The acquisition time was typically 5x10=50 s and was prolonged in the case of poor signal-noise ratio or it was shortened in the case of strong fluorescence or presence of organic material. Important prerequisites are that the Raman spectrometer gets calibrated before first use and that the ambient light is as low as possible in order to not interfere with the measurements. The mineral is typically measured along several axes. After the measurement, the data needs to be transferred to a computer with PeakFit™ installed. PeakFit™ is used to analyze precise peak position from the measured data (Enwave SLSR-PROTT Analyser operating manual).

4.3 Experimental calibrations The difference in wavenumbers of the main peaks of a mineral may be caused by impurities (for example, by metal ions or organic impurities) or by a distortion in mineral’s crystal lattice. The distortion in the lattice is caused either by fracturing, residual stress or by intracrystalline plasticity. Blenkinsop (2000) explains that the main mechanism behind the intracrystalline plasticity is applied dislocation motion, during which the crystal was in solid state of diffusion. In other words, the dislocation is a defect in the crystalline lattice. This type of the dislocation is the line representing a cut in the lattice, where an extra plane with extra atoms is accommodated. Due to the presence of the extra plane, the lattice is stretched, which causes the distortion. Raman spectroscopy can show if a lattice has a defect or contains an impurity. However, to be sure that instrumental effects do not create the wavenumber shifts, it is necessary to perform a calibration procedure.

Dubessy at al. (2012) describes the response of the spectrometer as a function of the laser power, the wavelength, the properties of the detector, the quality of the optics, the grating and the polarization of the scattered light. Raman shift wavenumbers are calculated in the relationship to the laser wavelength excitation. The dispersed Raman light – the flow of photons – is measured through grating by a charge coupled device (CCD). The CCD contains 1600 highly sensitive photon detectors known as pixels. Through the calibration procedure, each pixel represents a certain wavenumber. Thus, the purpose of the calibration is to correlate the pixel numbers to the wavenumbers of the spectrometer.

4.3.1 Calibration procedure A second order curve-fitting polynomial series of spectrum peaks from the Enwave calibration sample (ECS) is used to compute the corresponding wavenumbers for each pixel in CCD. The ECS consists of a capsule with a yellow powder (Figure 2), included in the portable Raman system package.

Figure 2. Enwave calibration sample, ECS-1. The polynomial coefficients, or calibration coefficients, are calculated from a matching matrix – the input parameters – which are represented by pre-programmed peaks (Figure 3), obtained by a single scan of the ECS-1 sample.

Figure 3. Spectrum measurements from the Enwave Calibrational Sample -1 (ECS-1). The values of the corresponding pixels need to be checked and recorded manually (Figure 4) into the input parameters window. The input parameters are required to calculate the calibration coefficients. When the calibration coefficients are calculated, the calibration procedure is completed.

Figure 4. The input parameters window with recorded pixels and calculated calibration coefficients. After the calibration procedure, the correlation between the pixels and the wavenumbers is adjusted and registered in a calibration file, which can be used in a case of re-calibration, if necessary.

4.4 PeakFit™ software PeakFit™ for Win32 v4 by AISN Software Inc. (PeakFit™) is an automated nonlinear peak separation and analysis software for spectroscopy, chromatography and electrophoresis. In this project, PeakFit™ was used for every mineral sample to find and fit peaks in the data from the Raman measurement with high precision. The peak fitting settings are chosen to: baseline – “Linear, D2, 3% tolerance”, smoothing – “Savitsky-Golay, 40.00%”, peak type – “Spectroscopy, Voigt Amp”, auto scan – “Amp 1.5%, Add Residuals checked, Vary Widths checked, Vary Shape checked” (the other settings were not tested). The peak fitting process is as follows (Figure 5). 1. A comma-separated file from the Raman measurement (with wavenumber and intensity values) is imported into PeakFit™. 2. A peak is selected for further analysis by cutting out a section of the graph in the visual interface, using the menu selection Prepare→Section function. 3. Autofitting mode is entered, using the menu selection AutoFit→AutoFit Peaks I Residuals. 4. All extra peaks besides the main peak are hidden by clicking on them in the visual interface. From the information in the lower left corner can be verified that only one peak is selected. 5. Numerical fitting is applied several times until the fit converges. If it doesn’t converge, numerical fitting is iterated until the Raman shift value does not change significantly. The numerical fitting function “Fast Peak Fit with Numerical Update” is accessed from the lower left corner. 6. The numerical fit is reviewed to extract the four parameters of interest: “Voigt Amplitude”, “FWHM”, “Std Error for Ctr” and “Intensity”. The review window is accessed by clicking “Review Fit” in the PeakFit™ Numerical Fitting window (5). 7. The process is repeated for every peak (2) that needs to be analyzed within the file. 8. The process is repeated for every measurement file (1).

Figure 5. PeakFit™ in operation.

4.5 Crystal Sleuth search engine CrystalSleuth was developed by the RRUFF group to lookup minerals by their Raman spectra. The software searches through the RRUFF database and presents likely mineral candidates that best match the given spectrum. There is a possibility to search by part of the spectrum by trimming it from the edges (Figure 6). This is useful when certain peaks need to be looked up individually (Lafuente et al., 2015). Unfortunately, the software works only if the mineral has a high-quality, undisturbed Raman spectrum, for example from a synthetic mineral. However, in complex cases that better match reality – having intergrowth of minerals, a fingerprint of the matrix, inclusions or presence of organic materials – the program does not work and requires manual matching. Manual matching was performed in 99.9% of all spectrum matching cases. Especially in the cases of unknown minerals, the program did not help.

Figure 6. CrystalSleuth in operation. 5 Chapter I – Carbonates

5.1 Background There are 277 carbonate-bearing minerals known today. Among them, 158 are pure carbonates and 119 additionally incorporate either of, or a combination of, the following anions: chloride, fluoride, borate, sulfate, phosphate, arsenate, arsenite, antimonate, silicate groups (Railsback, 1999). 2- Carbonates are anionic complexes of (CO3) and metallic cations with valences ranging from 1+ to 6+. The chemical bond connecting the metallic cation and the carbonate group is not as strong as the internal bond of the CO3 structure and can therefore be easily broken in the presence of hydrogen ions (Ahr, 2008). Carbonates with a simple chemical composition, containing Ca2+, Mg2+, and Fe2+ (calcite, dolomite, marble), are the most abundant carbonates and constitute together around 90% of natural occurrences, often found in extraterrestrial and in lacustrine sediments (Braithwaite, 2005). The majority of the hydrous carbonate minerals with more complicated chemical compositions are formed either by earth-surface alteration or by a combination of physical and chemical weathering (Railsback, 1999). According to the Dana's New Mineralogy by Richard V. Gaines, H. Catherine Skinner, Eugene E. Foord, Brian Mason, and Abraham Rosenzweig (1997), which is based on the chemical composition of minerals, carbonates can be divided into six main families: Acid

Carbonates, Anhydrous Carbonates, Hydrated Carbonates, Carbonates - Hydroxyl or Halogen (I), Carbonates - Hydroxyl or Halogen (II) and Compound Carbonates. Acid Carbonates are divided into smaller subclasses: • Borate

◦ Basic Hydrated

◦ Basic Hydrated Chloride

◦ Hydrated • Carbonate

◦ Basic Hydrated

◦ Hydrated • and detached acid carbonates with miscellaneous formulae.

Anhydrous Carbonates are divided into four main subclasses and 25 different groups (Figure 7).

Figure 7. Schematic representation of the Anhydrous Carbonates family of carbonate minerals. The Hydrated Carbonates family is divided into four main subclasses:

• Hydrated Carbonates where A+ (XO3) · x(H2O) (including Joliotite Group)

• Hydrated Carbonates where A+m B++n (XO3)p · x(H2O)

• Hydrated Carbonates where A+m B++n (XO3)p · x(H2O) and containing U, Th, Zr, Y (including Mckelveyite Group) • and Hydrated Carbonates (including Lanthanite Series).

Carbonates - Hydroxyl or Halogen (I) family is divided into: • Carbonates - Hydroxyl or Halogen in the Bastnasite/Shynchysite/Parasite Groups 14

• Carbonates - Hydroxyl or Halogen where (A B)3 (XO3)2 Zq • Carbonates - Hydroxyl or Halogen where (A B)2 (XO3) Zq (including Rosasite Group and Malachite Group) • Carbonates - Hydroxyl or Halogen where (A B)5 (XO3)2 Zq • and Carbonates - Hydroxyl or Halogen with miscellaneous formulae.

Carbonates - Hydroxyl or Halogen (II) family are divided into seven subclasses: • Carbonates - Hydroxyl or Halogen where (A)m (B)n (XO3)p Zq (including Ancylite group)

• Carbonates - Hydroxyl or Halogen where (A)m (B)n (XO3)p Zq · x(H2O) (including Dundasite Group)

• Carbonates - Hydroxyl or Halogen where Am Bn (XO3)p Zq · x(H2O)

• Carbonates - Hydroxyl or Halogen where (A)m (B)n (XO3)p Zq · x(H2O) • Carbonates - Hydroxyl or Halogen with miscellaneous formulae • Carbonates - Hydroxyl or Halogen (I) (including Sjorgrenite-Hydrotalcite Group (Sojogrenite Subgroup:Hexagonal), Sjorgrenite-Hydrotalcite Group (Hydrotalcite Subgroup:Rhombohedral), Sjorgrenite-Hydrotalcite Group (Hydrotalcite Subgroup:Rhombohedral), Quintinite - Charmarite Group) • and Carbonates - Hydroxyl or Halogen (II).

The last family, Compound Carbonates, has only one subclass: Compound Carbonates with miscellaneous formulae. It is divided into 15 smaller groups, among which two are the Tychite and Tundrite Groups (Mineralogy Database, 1997). Railsback (1999) divides carbonates based on the extent to which carbonate minerals - 2- - contain OH , O and/or H2O. Among pure carbonates, OH - and H2O-free minerals are those, which are built from monovalent, divalent, and at most a mixture of divalent and trivalent cations. While carbonate-bearing minerals, having a more complicated chemistry and highly - 2- charged trivalent cations, usually contain OH , O and/or H2O. According to the author, the minerals containing additional aforementioned anions also follow a certain pattern. For example, carbonates containing silicate groups generally also contain Ca2+ (they go in pair); F-bearing carbonates usually incorporate rare-earth cations; and phosphate-bearing carbonates all integrate monovalent or divalent cations in their structure. Railsback (1999) explains that spectroscopic properties of carbonate-bearing minerals are closely correlated to the mass or radius of the cations. The author describes a linear trend of

15 this correlation. For example, a Raman shift of the A1g internal vibration mode of the carbonate anion decreases with increasing cation radius, but with different slopes. Railsback (1999) also expresses belief that booming spectroscopic methods have a high chance to uncover far greater mineralogical diversity among the carbonate-bearing minerals than the traditional hypothesis would suggest. So why is it important to study this mineralogical diversity of the carbonate-bearing minerals? Firstly, the carbonates are one of the main contributors to the global carbon cycle. There is a growing assumption in the scientific world that some carbonates stay stable at the P-T conditions of the low mantle, and therefore represent an important source of carbon in the deep interior of the Earth. With the help of Raman spectroscopy, the depth from which a certain carbonate was brought up can be estimated. It can be achieved by investigation of potential residual stress in the mineral and by analysis of deviations from a usual Raman band (Spivak et al, 2014). Secondly, carbonates play an important role in the geochemical transfer between various reservoirs of our planet. For example, carbon is transferred from the planet's interior to the surface mainly by CO2 degassing at arc volcanoes, and the presence of carbonates during magma migration can result in a more explosive volcanic eruption (Deegan et al, 2016).

5.1.1 Anhydrous Carbonates

5.1.1.1 Anhydrous Carbonates with Simple Formula A + CO3

5.1.1.1.1 Calcite Group The Calcite Group is a group of minerals belonging to the bigger Carbonate Group with the general formula of MCO3, where "M" (metal) can be one or more of several positively charged metal ions M2+, specifically calcium, cobalt, iron, magnesium, zinc, cadmium, manganese and/or nickel. The metal ions are stacked with alternating layers of carbonate, 2- CO3 . The carbonate layers are represented by flat triangular shaped carbonate ions, with a carbon at the centre of the structure and three oxygens in each corner. This triangular structural element is a key feature in the trigonal symmetry of this group, 3 2/m. Minerals in this group (more specifically calcite, gaspeite, magnesite, otavite, rhodochrosite, siderite, smithsonite and sphaerocobaltite) are isomorphous with one another (belong to the same space group, R 3c) and have some specific properties in common. All minerals from the Calcite Group crystallise in the trigonal division of the hexagonal crystal system. They all form either rhombohedrons or scalenohedrons. They have a perfect rhombohedral cleavage

16 and demonstrate a strong double refraction in transparent rhombohedrons. The Calcite Group minerals can partially or fully replace one another, forming a solid solution series. For example, iron may take the place of magnesium in magnesite (MgCO3), transforming it to siderite (FeCO3), or they can coexist together in the intergrowth position (Guide to rocks, minerals and gemstones, (The Minerals and the Gemstones kingdom, 2016). It is assumed that the Calcite Group is in opposition to the Aragonite Group of minerals. The reason for this contrast is the fact that groups are dimorphous with one another, meaning that they have the same calcium carbonate chemistry, but different structures. Calcite crystallises by trigonal symmetry, whereas aragonite forms orthorhombic crystals. If the M- ion is larger than calcium, the mineral's structure will belong to the Aragonite Group, but if the M-ion is smaller than calcium, then the mineral's structure will be a part of the Calcite Group. The size of calcium remains the same in both groups, but different crystallisation temperatures, pressures and other physical and chemical circumstances will determine the crystal structure of either calcite or aragonite. However, aragonite is metastable relative to calcite and tends to convert to calcite if changes in environment allow for it (The Minerals and the Gemstones kingdom, 2016). The Calcite Group belongs to the Trigonal Hexagonal Scalenohedral Class in crystallography. The rhombohedron and the hexagonal scalenohedron are two principal forms in this class. In this class, the 3-fold rotoinversion axis corresponds to the vertical axis (c) and the three 2-fold rotation axes represent the three horizontal axes (a1, a2, a3) (Figure 8).

Figure 8. The axial configuration of the Trigonal Hexagonal Scalenohedral Class. Source: http://webmineral.com. Summarising the crystallographic properties of the Calcite Group, Table 2 should be mentioned.

Table 2. Crystallographic properties of the Calcite Group.

System Class name Axes Planes Centre Hermann- Space Maugin group Symbols Trigonal Hexagonal 2- 3- 4- 6- 3 yes 3 2/m R3c Scalenohedr Fo Fo Fo Fo

al ld ld ld ld 3 1 - -

5.1.1.1.1.1 Calcite (CaCO3)

Calcite is the most stable polymorph of calcium carbonates with the ideal formula CaCO3, though it often contains small amounts of magnesium, iron and manganese. The complex chemical composition has aroused investigations about phase relations in the system CaCO3 –

MgCO3, since the calcite-dolomite solvus can be used as a geological thermometer in petrologic studies. Besides, the chemical composition influences on the mineral’s stability at the variety of temperatures and pressures. Studies of Goldsmith & Newton (1969) showed that the presence of MgCO3 in the system increases the stability of calcite in comparison to aragonite. Though this effect is barely noticeable in the lower temperature range (up to 450°

C), it turns to be crucial at higher temperatures, where the difference between pure CaCO3 and

MgCO3 – saturated system grows larger. The same studies also demonstrated that at low temperatures (specifically room temperature) ionic substitution between CaCO3 (calcite) –

CaMg(CO3)2 (dolomite) – MgCO3 (magnesite) is very restricted. Trigonal-rhombohedral is considered to be the crystal system of calcite, yet calcite rhombohedral is rare as a natural crystal. Calcite shows diverse habits such as rhombohedra, tabular forms, prisms, and scalenohedra. It forms often solid granular masses and veinlets in sedimentary rocks, limestone in particular, as a result of accumulation of shells from dead marine organisms (Wenk & Bulakh, 2012). Calcite has 9 normal vibrations (3N - 6 = 3*5 -6 = 9), among which 5 vibrations are Raman active, 3 vibrations correspond to 2-fold rotation of the molecule and 1 vibration corresponds to 3-fold rotation of the molecule (Table 2 and 3, Figure 9).

Table 3. Raman active modes.

Atom WP A1g A1u A2g A2u Eu Eg O 18e 1 3

Mg 6b ------C 6a - - - - - 1

Ag – Symmetric with respect to principal axis of symmetry and symmetric with respect to inversion

Au – Symmetric with respect to principal axis of symmetry and anti-symmetrical with respect to inversion

Eg – Doubly generated, two-dimensional irreducible representation and symmetric with respect to inversion

Eu – Doubly generated, two-dimensional irreducible representation and anti-symmetrical with respect to inversion Total number of modes:

1A1g + 4Eg = 5

Figure 9. Compiled and normalised RRUFF data on calcite: R040070 (Source: University of Arizona Mineral Museum 6965, Locality: Pryor Mountain, Big Horn County, Montana, USA), R040170 (Source: University of Arizona Mineral Museum 13604, Locality: Peramea, Lerida Province, Catalonia, Spain), R050048 (Source: University of Arizona Mineral Museum 14020-93, Locality: Magdalena, New Mexico, USA), R050009 (Source: Eugene Schlepp, Locality: Amparo mine, Rodeo, Durango, Mexico), R050127 (Source: Dave Bunk Minerals, Locality: Rodeo, Durango, Mexico), R050128 (Source: Dave Bunk Minerals, Locality: Tie Siding, Albany County, Wyoming, USA), R050130 (Source: Dave Bunk Minerals, Locality: Mexico), X050034 (Source: 19

Caltech, Locality: unknown), X050035 (Source: G.R. Rossman 178, Locality: Hilton Deposit, San Diego County, California, USA), R050307 (Source: Eugene Schlepp, Locality: Zaire), R150020 (Source: Canan D'Avela, Locality: Creel, Chihuahua, Mexico), R150075 (Source: Michael Scott, Locality: Montana, USA). Table 4. Chemistry of the RRUFF samples. N Sample ID Chemistry Comments 1 R040070 (Ca0.99Mg0.01)C The most “contaminated”

O3 chemistry 2 R040170 (Ca0.99Mg0.01)C The most “contaminated”

O3; trace amounts chemistry of Co 3 R050048 (Ca0.99Zn0.01)C The most “contaminated”

O3 chemistry

4 R050009 Ca1.00CO3; trace amounts of Mn

5 R050127 Ca1.00CO3 The most ideal chemistry

6 R050128 Ca1.00CO3 Pseudomorph after aragonite, not single crystal. Trace of aragonite still present.

7 R050130 Ca1.00CO3; trace amounts of Si (?) 8 X050034 unknown

9 X050035 unknown

10 R050307 Ca1.00CO3 The most ideal chemistry

11 R150020 Ca0.993CO3; trace amount of Sr 12 R150075 unknown

-1 According to Rutt & Nicola (1974), calcite has two external modes: Eg at 155 cm and Eg at -1 -1 -1 281 cm ; three internal modes: Eg at 711 cm , A1g at 1085 and Eg at 1435 cm ; and one -1 combined 2v2 at 1748 cm . However, Cloots (1991) points out one more mode, a very weak satellite peak, located at 1039 cm-1 in the 1100-1000 cm-1 region, corresponding to the totally 2- symmetric stretch (v1) of the (CO3) anion. The nature of the satellite peak is still not fully

20 discovered. Cloots (1991) finds that the most probable explanation of this band presence is 18 16 18 enrichment in O or isotopic frequency of the v1 mode of the X O2 O ion.

5.1.1.1.1.2 Magnesite (MgCO3) Magnesite is an end member of the magnesite-siderite isomorphic series and it forms colourless, white, pale yellow, pale brown, faintly pink or lilac-rose crystals of different sizes. It crystalizes usually as the result of the alteration in ultramafic rocks, serpentinite, peridotite and other magnesium rich rock types due to both contact and regional metamorphism (Wenk & Bulakh, 2012). According to Gillet (1993), magnesite keeps its rhombohedral structure (R3c) unchanged even at the conditions of the transition zone and upper region of the Earth's lower mantle. It remains stable at depths of 100 to at least 1000 km in the Earth's mantle. Gillet (1993) applied different temperatures (up to 200 K) and pressures (up to 32 GPa) to magnesite samples and measured the structure of the mineral with the help of Raman spectroscopy. The Raman spectrum did not show any significant shifts, meaning that magnesite is also stable at pressure and temperature conditions that exist in subduction zones down to 600-800 km. This study was supported later by Spivak et al. (2014), where she and her team performed Raman study of MgCO3–FeCO3 carbonate solid solution at high pressures up to 55 GPa and came to the conclusion that magnesite does not show significant changes in any modes with increasing pressure. Magnesite has 9 normal vibrations (3N - 6 = 3*5 -6 = 9), among which 5 vibrations are Raman active; 3 vibrations correspond to 2-fold rotation of the molecule and 1 vibration corresponds to 3-fold rotation of the molecule. Magnesite, as well as the whole Calcite Group, has five Raman active modes: 1A1g + 4Eg = 5.

In earlier studies scientists distinguished six Raman frequencies for magnesite: external (Eg -1 -1 -1 -1 -1 =212 cm and Eg =328 cm ), internal (Eg = 739 cm , A1g = 1084 cm and Eg = 1445 cm ) -1 and the sixth, combination mode (A1g + Eg =1763 cm ) (Rutt & Nicola, 1974). Beside the -1 combination mode, which is often not detectable, the internal mode of A1g differs by 10 cm from modern studies. Today we distinguish five Raman active modes. Gillet (1993) distinguishes three Raman bands that represent the internal vibrations of the CO3 groups: ѵ1

-1 -1 -1 (1094 cm ), ѵ3 (1444 cm ) and ѵ4 (738 cm ) and two external vibrations. However, some modern studies are in agreement with Rutt & Nikola (1974) and differentiate six Raman frequencies for magnesite, the sixth one is linked to the combination of ѵ1 and ѵ4 (Boulard et al. (2012); Spivak et al. (2014)). Spivak et al. (2014) determined four Raman peaks which are

2- linked with internal vibrations of CO3 . The first one is the A1g symmetric stretch (ν1) at 1074/1092 and 1086–1092 cm−1 range (depending on the Mg and Fe concentration). This peak is also the highest intensity peak. The second one is the Eg vibration (ν4) at 720/737 and −1 −1 730–737 cm range and the asymmetric stretch Eg (ν3) 1425/1442 and 1427–1442 cm range, which had low intensity. The fourth one is 2ν2, which was also observed with low intensity at 1711/1759 and at 1733– 1758 cm−1. According to Spivak et al. (2014), two other −1 modes represent the lattice vibration: a transitional mode Eg (T) at 174/213 cm and a −1 2+ librational mode Eg (L) at 273/330 and 301–328 cm range. Mg is not Raman active and not visible on a spectrum (Figure 10, Table 3). Spivak et al. (2014) demonstrated with her studies that modes are shifted to low wave numbers with an increasing Fe concentration in the MgCO3–FeCO3 solid solution of the magnesite-siderite series. Correspondingly, with higher concentration of Mg, the Raman peak positions shift to higher numbers, because Mg2+ ions have smaller radius and lighter mass than Fe2+ ions (Boulard et al., 2012). The precise chemical composition plays an important role in this case. Iron, manganese, cobalt and nickel ions can occur in different concentrations in the magnesite structure. However, this dependence is not obvious for all peaks. Boulard et al. (2012) argues that ѵ1 and ѵ4 have poor Fe/Mg content correlation with the peak positions.

-1 However, the authors report that 2ѵ2 shows a large frequency variation of 37.9 cm and it is thus a good correlation between the Fe/Mg concentration and the peaks position.

Figure 10. Compiled and normalised RRUFF data on magnesite: R040114 (Source: University of Arizona Mineral Museum 7562; Locality: Snarum, Norway), R050443 (Source: CIT 2123; Locality: Serra Das Egnas, Brazil), R050676 (Source: CIT 1450; Locality: Gustine Merced County, California, USA), X050116 (Source: Eugene Schlepp; Locality: Brumado, Bahia, Brazil), X050116 (Source: University of Arizona Mineral Museum 3874; Locality: Tyrol, Austria). Table 5. Chemistry of the RRUFF samples. N Sample ID Chemistry Comments

1 R040114 (Mg0.98Fe0.01)C1.00O3

2 X050115 Unknown

3 X050116 Unknown

4 R050443 Mg1.00CO3 The most ideal chemistry 2+ 5 R050676 (Mg0.87Fe 0.12Ca0.01)Σ=1 The most “contaminated” sample

CO3; trace amounts of Mn and Cd; CO2 estimated by difference

5.1.1.1.1.3 Siderite (FeCO3) Siderite forms brown rhombohedral crystals with glassy luster. It contains iron, Fe2+ and 2- carbonate, CO3 . But beside main chemical components, it may incorporate zinc, magnesium and manganese. They can substitute the iron forming siderite-smithsonite, siderite-magnesite and siderite-rhodochrosite solid solution series. Siderite forms granular aggregates in hydrothermal medium-temperature veins, and is associated with barite, fluorite, galena and other minerals. More often siderite forms in sedimentary rocks at shallow burial depths at the late stage of hydrothermal alteration. Thus, the mineral's chemical composition is often dependent on the depositional environment of the enclosing sediments (Wenk & Bulakh, 2012). Recent Raman spectroscopy studies revealed that siderite stays also stable at great depth. Cerantola at al. (2015) performed a high-pressure spectroscopic study of siderite with a focus on spin crossover. Raman spectroscopy is sensitive to metal-to-ligand bond distance (M-L) between the high spin (HS) and low spin (LS) state vibrational modes. Thus, it is a useful technique to identify the predominant spin state in a system. Spin crossover takes place in some metal complexes due to external changes, such as a variation of temperature, pressure or an influence of a magnetic field. These studies show that spin transition in siderite would start

23 at much greater depths (>150 km) than it was previously believed, and goes over a depth range of at least 300–350 km instead of being a sharp discontinuity in the shallower part of the lower mantle. It is important to understand the physical and chemical properties of carbonate minerals at extreme conditions, because they represent hosts for carbon in the lower mantle and help to evaluate the deep carbon cycle. Moreover, Raman spectroscopy is able to show whether a specimen was subjected to significant pressure earlier, by identifying the residual stress in the form of Raman shifts in the band, or even by the presence of new peaks.

For example, Farfan et al. (2012) identified a new CO3 symmetric stretching mode at a 20 cm−1 lower frequency, beginning at approximately 46 GPa, and may stay as a residual stress even after the pressure is removed.

Siderite has also five Raman active modes in total: 1A1g + 4Eg = 5 (Figure 11, Table 5). -1 Rutt & Nicola (1974) distinguished five modes in their work: two external Eg at 195 cm and -1 Eg at 299 cm ; only two internal (in comparison to calcite and magnesite, which have three) -1 -1 -1 Eg at 731 cm and A1g at 1088 cm and one combinational mode (A1g + Eg) at 1738 cm .

They called siderite an unusual mineral and noted that the higher frequency internal Eg mode was not observed during an experiment, but instead a broad low intensity peak was detected in the region of 500 cm.1.

Figure 11. Compiled and normalised RRUFF data on siderite: X050143 (Source: Caltech; Locality: Invigtut, Greenland), R050349 (Source: California Institute of Technology; Locality: Litchfield County, Connecticut, USA), X050144 (Source: CIT 3247; Locality: near Rio de Janeiro, Brazil), R050262 (Source: Marcus Origlieri; Locality: Panasqueira mine, Barroca Grande, Beira Baixa, Portugal), R040034 (Source: University of Arizona

Mineral Museum 7584; Locality: Pribram, Czech Republic), X050145 (Source: Caltech 40298; Locality: Unknown). Table 6. Chemistry of the RRUFF samples. N Sample Chemistry Comments ID

1 R040034 (Fe0.72Mg0.24Mn0.03Ca0.01)Σ=1C1. Most “contaminated” sample

00O3; CO2 estimated by difference 2 X050143 Unknown

3 X050144 Unknown

4 X050145 Unknown

5 R050262 (Fe0.71Mg0.24Mn0.05)Σ=1CO3 ; light

: (Fe0.60Mg0.36Mn0.04)Σ=1CO3 ; intermediate :

(Fe0.54Mg0.42Mn0.04)Σ=1CO3 ; darker :

(Mg0.54Fe0.42Mn0.04)Σ=1CO3 darkest = magnesite

6 R050349 (Fe0.83Mg0.09Mn0.05Ca0.01)Σ=0.98C Most “contaminated” sample

5.1.1.1.1.4 Rhodochrosite (MnCO3) Rhodochrosite is another mineral belonging to the Calcite Group with manganese as the main metal ion and with the ideal chemical composition MnCO3. It is usually identified by its pink colour, but impurities can make the specimen white, grey or greenish-grey. Magnesium, zinc and calcium are often presented in the mineral lattice as impurities or distortion, since they frequently substitute for manganese in the structure, which may lead to the change of colour. The mineral forms a complete solid solution with siderite. Rhodochrosite can be found in the hydrothermal veins along with other manganese minerals in low temperature ore deposits of sedimentary origin (Wenk & Bulakh, 2012).

Rhodochrosite with ideal chemistry has five Raman active modes in total: 1A1g + 4Eg = 5 (Figure 12, Table 6). Rutt & Nikola (1974) identified six peaks for rhodochrosite in their

-1 -1 work: two external peaks Eg at 183 cm and Eg at 289 cm ; three internal modes Eg at 721 -1 -1 -1 -1 cm , A1g at 1088 cm and Eg at 1417 cm ; one combinational peak ((A1g + Eg) at 1729 cm .

Figure 12. Compiled and normalised RRUFF data on rhodochrosite: R040133 (Source: University of Arizona Mineral Museum 13417, Location: Imuris, Sonora, Mexico), R050019 (Source: Eugene Schlepp, Location: Home Sweet Home mine, Colorado, USA), R050116 (Source: He Xin Jian, Location: Wudong mine, Liubao, Guangxi Autonomous Region, China), X050138 (Source: G.R. Rossman 1858, Location: Colorado, USA), R100002 (Source: Marcus Origlieri, Location: Wudong mine, Liubao, Guangxi Autonomous Region, China), R100162 (Source: William W. Pinch, Location: N'Chwaning mine, Kuruman, Kalahari Mn area, Cape Province, South Africa). Table 7. Chemistry of the RRUFF samples. N Sample ID Chemistry Comments 1 R040133 (Mn0.92Mg0.02Ca0.01)C1.0 The most “contaminated”

2O3 sample

2 R050019 Mn1.00 CO3 The most ideal chemistry 3 R050116 Unknown

4 X050138 Unknown

5 R100002 Unknown

6 R100162 Unknown

5.1.1.1.2 Aragonite group

Aragonite group includes aragonite (CaCO3), witherite (BaCO3), strontianite (SrCO3) and cerussite (PbCO3). Aragonite group has an Orthorhombic – Dipyramidal crystal system. It has space group Pbnm and H-M Symbol is 2/m 2/m 2/m (Table 7). The cations are aligned in the minerals' structure almost in the manner of hexagonal closest-packing, creating a pseudohexagonal symmetry (Mineralogy Database, 1997).

Table 8. Summary of the crystallographic properties of the Aragonite Group. Source: www.webmineral.com. System Class Axes Planes Centre Hermann- Space name Maugin group Symbols

Orthorhombi Dipyramid 2- 3- 4- 6- 3 yes 2/m 2/m Pbnm 16 c al Fo Fo Fo Fo 2/m (D 2h) ld ld ld ld 3 - - -

Aragonite group has 30 predicted active Raman modes (Urmos et al., 1991). However, usually only half of them are really visible during experiment. Urmos et al., (1991) distinguished 14 bands during an experiment with various corals consisting of either calcite or aragonite. Buzgar & Apopei (2009) managed to register only five Raman bands during an experiment with aragonite group minerals.

There are six main expected Raman bands: T(M,CO3), ν1, ν2, ν3, ν4 and 2 ν1 (Buzgar & Apopei, 2009). The internal modes of the aragonite group can be calculated from the group analysis based on an orthorhombic crystal structure (Table 8) (Martens et al., 2004):

Γint= 4Ag + 2B1g + 4B2g + 2B3g + 2Au + 4B1u + 2B2u + 4B3u

Table 9. All g-modes are Raman active and all u-modes are infrared active. Modified after Martens et al., 2004.

Free symmetry Factor group (Cs) Activity

V1 4Ag, 4B2g Raman

V2 4B1u, 4B3u IR

V3 2B1g, 2B3g Raman

V4 2Au, 2B2u IR

5.1.1.1.2.1 Aragonite (CaCO3)

Aragonite is one of the five known polymorphs of calcium carbonate: the hydrated phases ikaite and monohydrocalcite, anhydrous calcite, aragonite and vaterite. But only three are naturally occurring: aragonite, anhydrous calcite and vaterite (Parker et al., 2010; French et al., 1980). Single crystals of aragonite are tabular or prismatic with pseudohexagonal symmetry. The colouring is usually white, yellowish-white, brown, or grey (Wenk & Bulakh, 2012). Aragonite forms often on the interior walls of limestone caves. It crystallises in the oxidation zone of sulphide ores and weathering crust, precipitates biologically in marine environments by rich marine fauna (Wenk & Bulakh, 2012; Parker et al., 2010). Raman spectroscopic band of aragonite governs by the Aragonite group symmetry and is expressed by external and internal modes. External modes of aragonite are not reported by all authors (see table below). French et al. (1980) work is among the few studies giving a complete picture of aragonite's lattice motion. The author reports that external modes are 2+ 2- determined by the translational motion of Ca , translational and rotational motion of CO3 .

The Raman active external modes are: 5Ag + 5B2g + 4B1g + 4B3g.

The internal modes are characterised by V1, V2, V3 and V4 phases. The Raman active internal modes are represented by 4Ag + 2B1g + 4B2g + 2B3g. According to the literature, V4 -1 2- peaks come between 701 and 721 cm . V2, the result of bending and stretching of CO3 , has -1 -1 Ag at 853-854 cm , but B2g was reported only by a few authors and it is located at 907 cm

(French et al.,1980). V1 has almost the same story, where only Ag is reported by various -1 authors in the range 1054 to 1085 cm , however, B2g still remains undiscovered. V3, 2- antisymmetric C-O stretching of CO3 , is represented by Ag, B1g, B2g and B3g. Here, B1g has never been recorded and mentioned in literature (Table 9 and 10, Figure 13).

Table 10. This table summarises a few studies on the Raman spectroscopy of aragonite: Buzgar & Apopei (2009), Urmos (1991), Krishnamurti (1960), Martens et al. (2004) and Frech et al. (1980). Buzgar & Urmos Krishnam Martens et Frech et al. (1980) Assignment Apopei (1991) urti al (2004) (2009) cm-1 (1960) cm-1 cm-1 cm-1

250 284 285 No Ag: 142, 161, 193, T(M,CO3)

214, 284; B1g: External

112, 152; B2g: 180, modes

206, 248; B3g: 123, 190, 272

701 701 702 701 701 ν4 Ag

No 705 707 705 705 B2g

No No 716 721 B1g

721 B3g

No 853 854 853 853 ν2 Ag

No No No No 907 B2g

1083 1085 1086 1054 1085 ν1 Ag

No No No No No B2g

No No No No No ν3 B1g

1461 1462 1415 No No B2g

1573 1547 1463 1461 1462 Ag

No No No No 1574 B3g

No No 2165 No No 2ν1

Figure 13. Compiled and normalised RRUFF data on aragonite: R040078 (Source: University of Arizona Mineral Museum 3887, Locality: Molina, Aragon, Spain), X050023 (Source: Caltech, Locality: Spain), R060195 (Source: Marcus Origlieri, Locality: Cicov Hill, Horenec, Czech Republic), R080142 (Source: Renato and Adriana Pagano, Locality: Miniere di Brosso, Ivrea, Torino, Italy), R150021 (Source: Canan D'Avela, Locality: Gallo river, Molina de Aragón, Guadalajara, Castile-La Mancha, Spain). Table 11. Chemistry of the RRUFF samples. N Sample ID Chemistry Comments

1 R040078 Ca1.00 CO3 The most ideal chemistry 2 X050023 Unknown

3 R060195 Ca1.00 CO3 The most ideal chemistry

4 R080142 (Ca0.96 Sr0.02)Σ=0.98 CO3 The most “contaminated” sample

5 R150021 (Ca0.987Sr0.0096) CO3 The most “contaminated” sample

5.1.1.1.2.2 Cerussite (PbCO3) Cerussite is a secondary product of lead ore oxidation, despite the fact that it is the lead ore, it not the important one. Cerussite crystallizes in the orthorhombic system and forms fine- grained and dense semi-transparent gray, grayish-white or black aggregates of crystals. It is isomorphous with aragonite and is therefore twinned with aragonite, and creates a pseudohexagonal symmetry (Wenk & Bulakh, 2012). Raman spectroscopy of cerussite is governed by its aragonite structure, with a significant difference in the radius of the metallic ion. In general, Raman bands of aragonite and cerussite 2+ 2- are alike. Modes of transition of the Pb and CO3 along different axis represent the external modes, the lattice vibration. Minch et al. (2010) managed to identify five Raman bands representing external modes. Martens et al. (2004) registered nine external modes in the range -1 2- between 120 and 243 cm . According to the literature, the Raman active V4, bending of CO3

, is observed usually at all four internal modes (Ag, B1g, B2g, B3g) (Martens et al., 2004; Minch 2- et al., 2010). V1 and V2 are associated with bend and stretching of CO3 . Raman active Ag is usually easily registered, but B2g has been almost never reported. Martens et al. (2004) explains this phenomenon by the small coupling between the Ag and B2g modes. V3 represents anti-symmetric stretching internal mode and is usually detected in all four cases: Ag, B1g, B2g -1 and B3g. Some authors have also reported small satellite bands at 823 and 1031 cm . Martens et al (2004) explains this phenomenon by the isotopic substitutions of 13C and 18O (Table 11 and 12; Figure 14).

Table 12. This table summarises a few studies on the Raman spectroscopy of cerussite: Martens et al. (2004) and Minch et al. (2010). Martens et al. Minch et al. (2010) Assignment (2004) cm-1 cm-1 2+ 2- 120, 132, 148, 152, 114.6; 130.2; 148.3; T(M,CO3): translation of the Pb and CO3 2- 174, 179, 213, 226, 173; 218.5 along different axis; rotation of CO3 (External 243 modes)

2- 668 671.2 V4 B3g (V4-in-plane of CO3 groups)

673 675.8 A1g

694 683.8 B2g

681 696.6 B1g 2- 837 839.2 V2 A1g (V2-out-of-plane band of CO3 )

No No B2g

1054 1054.5 V1 A1g (V1-symmetric C-O stretching of 2- No No CO3 groups)

B2g

1361 1371.3 V3 A1g (V3 – asymmetric C-O stretching of 2- 1376 1421.3 CO3 groups)

1477 1478.1 B1g

1419 No B2g

B3g

No No 2V1

Figure 14. Compiled and normalised RRUFF data on cerussite: R040069 (Source: University of Arizona Mineral Museum 4206, Locality: Broken Hill, New South Wales, Australia), R050011 (Source: Eugene Schlepp, Locality: Daoping Lead and Zinc mine, Gongcheng, Guangxi, China), R050023 (Source: Eugene Schlepp, Locality: Mammoth - St Anthony mine, Tiger, Pinal County, Arizona, USA), R050174 (Source: Marcus Origlieri, Locality: Tsumeb mine, Tsumeb, Otavi District, Oshikoto, Namibia), R050298 (Source: Eugene Schlepp, Locality: Bunker Hill mine, Shoshone County, Idaho, USA), R060017 (Source: American Museum of Natural History 34137, Locality: Gonessa, Sardinia, Italy).

Table 13. The RRUFF database of cerussite samples is represented by minerals with only ideal chemical composition. There is no single mineral in the RRUFF database with “contaminated” chemistry. N Sample ID Chemistry Comments

1 R040069 Pb1.04 C0.98 O3 The most ideal chemistry

2 R050011 Pb1.00 CO3 ; CO2 not measured but The most ideal chemistry estimated by difference and stoichiometry

3 R050023 Pb1.00 CO3 ; CO2 not measured but The most ideal chemistry estimated by difference and stoichiometry

4 R050174 Pb1.00 CO3 ; C not measured but The most ideal chemistry estimated by difference and stoichiometry

5 R050298 Pb1.00 CO3 The most ideal chemistry

6 R060017 Pb1.00CO3 ; C not measured but The most ideal chemistry estimated by difference and

stoichiometry

5.1.1.1.2.3 Witherite (BaCO3) Witherite, another mineral of the Aragonite group, has the orthorhombic crystal system with pseudo-hexagonal symmetry. The mineral can be colourless, milky-white, grey, pale-yellow, green or pale-brown. Witherite is the second most common barium mineral, but it is found only at a few locations. Witherite can contain a small amount of Ca, but is has a complete solid solution with strontianite, not with aragonite (Martens et al., 2004). The mineral crystallises in low-temperature hydrothermal environments and is the result of action of carbonated waters on pre-existing barite (Chamberlain et al., 1986). Raman spectroscopy of witherite is governed by its aragonite structure. The main deviations are coming from the bigger radius of Ba2+ ion. Thus, the cell parameters of witherite are greater than those of aragonite. In general, Raman bands of aragonite, cerussite and witherite are alike (Martens et al.,2004) (Table 13 and 14, Figure 15).

Table 14. This table summarises a few studies on the Raman spectroscopy of witherite: Buzgar & Apopei (2009), Beny (1989), Krishnamurti (1960) and Martens et al. (2004). Buzgar & Beny (1989) Krishnamurti Martens et al. Assignment Apopei (2009) cm-1 (1960) (2004)

32 cm-1 cm-1 cm-1

227 227 224 No T(M,CO3)

693 691 690 ν4 Ag

No 699 696 B2g

No No No B1g

B3g

No 852 No 847 ν2 Ag

B2g

1059 1061 1035 No ν1 B2g

1059 1060 Ag

No 1394 No No ν3 combinat.

1422 1409 1419 1420 Ag

1511 1421 1505 1450 B2g

1509 B1g

1539 B3g

No 2116 No No 2ν1

Figure 15. Compiled and normalised RRUFF data on witherite: R040040 (Source: University of Arizona Mineral Museum 8505, Locality: Cave-in-Rock, Hardin County, Illinois, USA), R050148 (Source: Jim McGlasson, Locality: Settlingstones mine, Fourstones, Northumberland, England), R050267 (Source: Marcus Origlieri, Locality: Fallowfields mine, Alston Moor, England). Table 15. Chemistry of the RRUFF samples. All three RRUFF samples contain Sr.

N Sample ID Chemistry Comments

1 R040040 (Ba0.98Sr0.02)Σ=1CO3; CO2 “contaminated” estimated by difference chemistry

2 R050148 (Ba0.96Sr0.04)CO3 “contaminated” chemistry

3 R050267 (Ba0.96Sr0.04)CO3 “contaminated” chemistry

5.1.2 Anhydrous Carbonates with Compound Formula A + B ++ (CO3)2

5.1.2.1 Dolomite group

The Dolomite group includes four minerals: dolomite (CaMg(CO3)2), ankerite

(Ca(Fe++,Mg,Mn)(CO3)2), kutnohorite (Ca(Mn,Mg,Fe++)(CO3)2) and minrecordite

(CaZn(CO3)2). Members of this group have a related crystal structure to that of calcite. However, in the Dolomite group, layers of Ca and Mg (Fe++, Mn or Zn) alternate along the c- axis, which destabilizes the structure and lowers the crystal symmetry from 32/m to 3. The symmetry system is Trigonal-Rhombohedral with space group R 3 3 (Table 15).

Table 16. Summary of the crystallographic properties of the Dolomite Group. Source: www.webmineral.com. System Class name Axes Planes Centre Hermann- Space Maugin group Symbols Trigonal Rhombohedr 2- 3- 4- 6- - yes -3 R 3 3

al Fo Fo Fo Fo ld ld ld ld - 1 - -

Raman spectroscopy of the Aragonite group is governed by its Trigonal-Rhombohedral 2- mineral structure and is characterized by motions of CO3 . The main deviations originate from the difference of the radii of the metallic ions of Mg, Fe and Zn (Table 16).

Table 17. Factor analysis of the Dolomite group gives 8 Raman active modes (4Ag + 4Eg) and 12 IR active modes (6Au + 6 Eu). Modified after Gunasekaran et al., 2006. Type Total modes Lattice modes Internal modes Activity

Ag 4 2 V1 + V2 Raman

Eg 4 2 V3 + V4 Raman

Au 6 3 V1 + V2 IR

Eu 6 3 V3 + V4 IR

5.1.2.1.1 Dolomite CaMg(CO3)2 Dolomite has white or brownish-grey rhombohedral crystals. Dolomite creates two series of solid solutions: one solid solution with calcite, but only at high temperatures, and one solid solution with ankerite (Ca(Fe++,Mg,Mn)(CO3)2) (Wenk & Bulakh, 2012). The Raman spectroscopic band of the dolomite is characterised by external (translational movement of Ca, Mg and CO3) and internal modes. The intensity and the precise position of the Raman peaks depend on the chemical composition of the mineral. If a dolomite sample contains, along with Ca and Mg, another metallic ion, it forms more distortions, shaping the Raman band differently. For example, a comparison between the RRUFF samples X050062 and R040030 shows additional peaks in the Raman band of X050062 in the area between 1100 and 1500 cm-1. The most probable explanation is that X050062 has an additional metallic ion incorporated in the mineral lattice, while R040030 has an almost ideal chemical composition (Table 17 and 18, Figure 16).

Table 18. The internal Raman modes are represented by V1, V2, V3, V4 and their combinations (V1 + V2, 2V2 + V4 and 2V3). Gunasekaran et al., Huang & Kerr, 1960 Assignment 2006 (cm-1) (cm-1)

187 179 T(Ca, Mg, CO3)

309 304 T(Ca, Mg, CO3)

733 725 V4- Symmetric CO3 deformation

No No V2- Asymmetric CO3 deformation

1106 1100 V1- Symmetric CO3 stretching

1450 1445 V3- Asymmetric CO3 stretching

1765 No V1 + V4

- No 2V2 + V4

- No 2V3

Figure 16. Compiled and normalised RRUFF data on dolomite: R040030 (Source: University of Arizona Mineral Museum 1961, Locality: Austria), R050129 (Source: Dave Bunk Minerals, Locality: Black Cloud mine, Leadville, Lake County, Colorado, USA), X050062 (Source: CIT 9356, Locality: Chitwood, Missouri, USA), X050063 (Source: CIT 12849, Locality: Sunk Magnesite mine, near Trieben, Steiermark, Austria), R050241 (Source: Marcus Origlieri , Locality: Eugui quarries, Navarre, Spain), R050272 (Source: University of Arizona Mineral Museum 13548, Locality: Eagle mine, Gillman, Colorado, USA), R050357 (Source: California Institute of Technology , Locality: Black Rock, Lawrence County, Arkansas, USA), R050370 (Source: Eugene Schlepp, Locality: Morro Velho mine, Nova Lima, Minas Gerais, Brazil), R100118 (Source: Ray Hill and Robert Woodside, Locality: Bay Mag mine, Mount Brussilof, British Columbia, Canada), R100168 (Source: Mineralogical Museum, Harvard University 105064, Locality: Oberdorf An Der Laming Moine near Bruck An Der Mur, Styria, Austria). Table 19. Chemistry of the dolomite RRUFF samples. There is no sample with absolutely ideal chemical composition. N Sample ID Chemistry Comments

1 R040030 (Ca0.99Mg0.01)Σ=1Mg1.00(CO3)2 ; trace amounts of The closest to the

Mn; CO2 estimated by difference ideal formula

2+ 2 R050129 Ca(Mg0.62Fe 0.33Mn0.05)Σ=1(CO3)2 ; CO2 estimated by difference 3 X050062 Unknown

4 X050063 Unknown

2+ 5 R050241 (Ca0.96Mg0.04)Σ=1(Mg0.98Fe 0.02)Σ=1(CO3)2 ;

CO2 estimated by difference

2+ 2+ 2+ 6 R050272 (Ca0.96Fe 0.04)Σ=1(Mg0.63Mn 0.21Fe 0.16)Σ=1(CO3)2 ; The most

CO3 estimated by difference and “contaminated” stoichiometry

2+ 7 R050357 Ca1.00(Mg0.98Fe 0.02)Σ=1(CO3)2 ; CO2 estimated by

difference

8 R050370 (Ca0.84Fe0.16)Σ=1(Mg0.98Mn0.02)Σ=1(CO3)2 ;

CO2 estimated by difference 9 R100118 Unknown

10 R100168 Unknown

5.1.3 Anhydrous Carbonates with Compound Formula A+2 B++2 (CO3)4

5.1.3.1 Burbankite Group (Hexagonal) The Burbankite group (Hexagonal) differs from other Anhydrous Carbonates by a more complicated chemical composition, A+2 B++2 (CO3)4.. This group includes four minerals: burbankite ((Na, Ca)3(Sr,Ba,Ce)3(CO3)5), khanneshite ((NaCa)3(Ba,Sr,Ce,Ca)3(CO3)5), calcioburbankite (Na3(Ca,REE,Sr)3(CO3)5) and sanromanite (Na2CaPb3(CO3)5). Burbankite (Hexagonal) group has the Hexagonal - Dihexagonal Dipyramidal class of symmetry. It means that this group has a hexagonal system with a vertical hexad axis, six horizontal diad axes, six vertical planes and a horizontal plane of symmetry, creating totally 7 planes with a centre. The space group is P 63/mmc (Table 19) (Mineralogy Database, 1997).

Table 20. Summarising the crystallographic properties of the Burbankite Group. Source: www.webmineral.com. System Class Axes Planes Centre Hermann- Space name Maugin group Symbols Hexagona Dihexagon 2- 3- 4- 6- 7 yes 6/m 2/m P l al Fo Fo Fo Fo 2/m 63/mmc Dipyramid ld ld ld ld

al 6 - - 1

5.1.3.1.1 Burbankite (Na, Ca)3(Sr,Ba,Ce)3(CO3)5 The rare-earth carbonate mineral burbankite differs from the majority of carbonates by the complexity of its chemical composition. The mineral's lattice incorporates the univalent cation Na+ together with a whole series of divalent cations (Ca, Sr, Ba) and rare earth elements (e.g.

Nd, La). The common ratio of cations to CO3 is 6:5, so the general formula of burbankite can

37 be expressed as Q6(CO3)5. The complex chemical composition affects in its turn the crystal structure. The complex structure of burbankite is an anomaly, especially in comparison to other Anhydrous Carbonates. Burbankite has two crystallographically different groups of cations (A and B) in the same structure. The A-cations form eight-pointed complicated figures, which consist of a distorted trigonal prism and four-sided pyramids, where the pyramids are placed on the prism's two faces. The B-cations build a ten-pointed polygon with twelve triangular and two quadrangular faces. Furthermore, the burbankite's structure incorporates three crystallographically independent CO3 triangles oriented differently in space (Voronkov & Shumyatskaya, 1968; Pecora & Kerr, 1953). The mineral was discovered in the late 50s, so there are works dedicated to the investigation of its Raman spectrum. In his work, Buhn et al. (1999) discusses the main peak of burbankite's Raman spectrum, located at 1078 cm-1. The authors compare burbankite's main peak with the peak of calcite, which is located at 1086 cm-1. The authors point out that burbankite's peak is significantly broader and shifted towards lower wave numbers. Generally speaking, the Raman band of burbankite is characterised by a broad peak in the area between 200 to 300 cm-1, by a small broad peak in the area around 700 cm-1, by a broad peak in the area around 900 and 1000 cm-1 and by the strongest peak at 1078 cm-1 (Figure 17,

Table 20). Analogous with the Calcite group, the strongest peak is represented by V1 (Ag), the broad peak in the area between 200 and 300 cm-1 is responsible for the external mode (lattice -1 motion), the small peak at approximately 700 cm represents V4 (Ag), while the broad peak in -1 the area between 900 and 1000 cm is created by V1 (Ag) motion.

Figure 17. Compiled and normalised RRUFF data on burbankite: R050646 (Source: Marcus Origlieri, Locality: Cerro Sapo, Cochabamba Department, Bolivia), R110199 (Source: Donald Doell, Locality: Poudrette quarry, Mont Saint-Hilaire, Quebec, Canada), R120073 (Source: Donald Doell, Locality: Mont Saint-Hilaire, Rouville RCM, Montérégie, Québec, Canada). Table 21. There is only one burbankite sample with detailed chemical composition at the RRUFF database, Sample R050646. N Sample ID Chemistry Comments

1 R050646 (Na2.03Ca0.97)Σ=3(Sr3.14Ba0.18Ce0.17 0.15Th0.10Nd0.08La0.08)Σ=3(CO3)5 ; light-gray:

(Na1.97Ca1.03)Σ=3(Sr1.87 0.40Ba0.37Ce0.14Th0.11Nd0.06La0.05)Σ=3(CO3)5 ; C estimated by stoichiometry 2 R110199 Unknown

3 R120073 Unknown

5.1.4 Carbonates - Hydroxyl or Halogen (I)

5.1.4.1 Carbonates - Hydroxyl or Halogen where (A B)2 (XO3) Zq

5.1.4.1.1 Malachite Group

The Malachite group contains four minerals: malachite (Cu2(CO3)(OH)2), nullaginite

(Ni2(CO3)(OH)2), pokrovskite (Mg2(CO3)(OH)2 · 0.5(H2O)), and chukanovite

(Fe2(CO3)(OH)2). Apart from malachite, this group contains uncommon, rare minerals. For example, pokrovskite, named after the Russian mineralogist Pokrovskij, is an uncommon mineral usually found in ultramafic dunite (an igneous rock largely consisting of olivine) or serpentinite. So far, it has only been discovered in a handful of places in Kazakhstan and in the United States (Dakota Matrix Minerals, 1998). Nullaginite is even rarer. This mineral is named after the Otway nickel deposit in the Nullagine (Western Australia). Just after the discoveryin the late 70s, scientists related it to the Rosasite group. Only later studies revealed that it belonged to the Malachite group. However, there is still no common opinion on this issue. Some scientists even today believe that this mineral should belong to the Rosasite group. Nullaginite is only found in Western Australia and Tasmania. It forms nodular grains and cross-fibre veinlets in oxidized nickel-bearing hydrothermal ore deposits (Nickel & Berry, 1981). Minerals from this group build the monoclinic-prismatic crystal system. The monoclinic system can be described as a system with three vectors of unequal lengths, which form a

39 rectangular prism with a parallelogram as its base. Minerals with monoclinic-prismatic system have a centre of symmetry, but they have only one plane and have Space Group P 21/a (Table 21) (Mineralogy Database, 1997).

Table 22. Summary of the crystallographic properties of the Malachite Group. Source: www.webmineral.com. System Class Axes Planes Centre Hermann- Space name Maugin group Symbols

Monoclini Prismatic 2- 3- 4- 6- 1 yes 2/m P 21/a c Fo Fo Fo Fo ld ld ld ld 1 - - -

5.1.4.1.1.1 Malachite Cu2(CO3)(OH)2 Malachite is a second basic carbonate of copper, found in the oxidation zone of chalcopyrite and other copper sulphide deposits. Malachite crystallises often as a thin coating in fractures and builds sometimes kidney-shaped aggregates (Wenk & Bulakh, 2012). The most characteristic feature of the mineral is its bright green colour. Due to its beautiful colour, malachite has been used intensively in art works throughout the whole history of mankind. In this context, Raman spectroscopy is therefore not only important to mineralogists, but also to archaeologists (Frost et al., 2002). The Raman band of malachite shows two strongest and characteristic peaks. The first one is at approximately 435 cm-1 (it varies between different authors from 429 to 435 cm-1) and the second is at approximately 1495 cm-1 (it varies between different authors from 1493 to 1497 cm-1) (see table below). The fist strongest peak represents the external mode, while the second strongest peak is characteristic for the asymmetric stretching of CO3 (V3). Other peaks represent V1 (symmetric CO3 stretching mode), V2 (asymmetric CO3 bending mode), V4

(symmetric CO3 bending mode) and two modes of the hydroxyl group (Buzgar & Apopei, 2009; Yu et al., 2013). However, two samples from the RRUFF database do not show all of malachite's peaks. Only one characteristic malachite peak is visible in the Raman band in the area around 435 cm-1. Unfortunately, both RRUFF samples miss the area from 1200 cm-1 and on (Table 22 and 23, Figure 18).

Table 23. Summary of a few studies on Raman spectroscopy of malachite: Buzgar & Apopei (2009), Frost et al. (2002), Mattei et al. (2008) and Yu et al. (2013).

Buzgar & Frost et al. Mattei et al. Yu et al. Assignment Apopei (2009) (2002) (2008) (2013)

215, 269, 354, 434, 130, 142, 151, 166, 157, 171, 182, 204, 143, 179, 221, 270, T(Cu, CO3) 536, 596 176, 205, 217, 267, 224, 272, 352, 435, 352, 432, 510, 535, 294, 320, 249, 389, 513, 537, 601 566, 598 429, 514, 531, 563, 596

722 718 723 719 ν4-Symmetric CO3 755 750 753 751 bending mode

820 807 815 ν2-Asymmetric CO3 817 bending mode

1059 1098 1058 1060 ν1-Symmetric CO3 1097 1101 1096 stretching mode

1368 1365 1370 1367 ν3-Asymmetric CO3 1462 1423 1463 1459 stretching mode 1495 1493 1497 1493 1514

1639 O-H bending mode

3310 3349 3309 O-H stretching mode 3382 3380 3380 3380

Figure 18. Compiled and normalised RRUFF data on malachite: R050531 (Source: University of Arizona Mineral Museum 4809, Locality: Tsumeb mine, Tsumeb, Otavi District, Oshikoto, Namibia), R050508 (Source: University of Arizona Mineral Museum 12261, Locality: Kambova, Kantanga, Zaire). Table 24. Chemistry of the malachite RRUFF samples. N Sample ID Chemistry Comments

1 R050531 (Cu1.95Zn0.05)Σ=2(CO3)(OH)2 ; C not It has Zn incorporated in measured but estimated by the structure stoichiometry

2 R050508 Cu2.00(CO3)(OH)2 The most ideal chemistry

5.1.5 Carbonates - Hydroxyl or Halogen (II)

5.1.5.1 Carbonates - Hydroxyl or Halogen where (A)m (B)n (XO3)p Zq, with (m+n):p=1:1

5.1.5.1.1 Ancylite group

The Ancylite group contains seven minerals: ancylite-(Ce) SrCe(CO3)2(OH)·(H2O), calcioancylite-(Ce) CaCe(CO3)2(OH)·(H2O), calcioancylite-(Nd) CaNd(CO3)2(OH)·(H2O), gysinite-(Nd) Pb(Nd,La)(CO3)2(OH)·(H2O), ancylite-(La) Sr(La,Ce)(CO3)2(OH)·(H2O), kozoite-(Nd) (Nd,La,Sm,Pr)(CO3)(OH) and kozoite-(La) La(CO3)(OH). All minerals in the Ancylite group are rare and were discovered comparatively recently. For example, kozoite – (Nd) was discovered in 1997 in Japan. The crystals do not exceed 10 µm in size, so they can

42 only be recognised through a microscope. Hitherto, kozoite-(Nd) was only found in alkali olivine basalt in the Niikoba area in Japan. It is assumed that the mineral was formed from postmagmatic hydrothermal activity. But more studies are needed in order to clarify this issue (Miyawaki et al., 2000). The crystal structure of ancylite can be compared to the orthorhombic structure of the aragonite group. The lattice system of the Ancylite group is Orthorombic-dipyramidal with three planes, and with a centre of symmetry. The various metal ions in the structure are located in a ten-vertex polyhedral system, forming a three-dimensional framework with a hydroxyl group, lying on the mirror plane to the orthorhombic lattice and bonded to the heavy cations. (Table 24, Figure 19) (Belovitskaya et al., 2002; Dal Negro et al., 1975).

Table 25. Crystallographic properties of the Ancylite group. The Space group is Pmcn. Source: www.webmineral.com. System Class Axes Planes Centre Hermann- Space name Maugin group Symbols

Orthorhombi Dipyramid 2- 3- 4- 6- 3 yes 2/m 2/m Pmcn c al Fo Fo Fo Fo 2/m ld ld ld ld 3 - - -

Figure 19. Projection of an ideal ancylite structure onto the (100) plane. Modified after Belovitskaya et al., 2002.

5.1.5.1.1.1 Ancylite-(Ce) SrCe(CO3)2(OH)·(H2O)/ ancylite-(La) Sr(La,Ce)(CO3)2(OH)·(H2O) Ancylite can be of two types, ancylite-(Ce) and ancylite-(La). They are separated on the basis of the Sr/La ratio in their chemical composition. The mineral is usually found in pegmatites of alkaline rocks or as an accessory mineral in nepheline syenite and carbonatites. The mineral was identified in Greenland, Canada, the United States, Russia, Norway, China, Brazil, and the Democratic Republic of Congo (Dal Negro et al., 1975). All RRUFF ancylite samples belong to the Ce-group, though all contain a small amount of La. The sample R060205 additionally contains Ba2+, whereas R060218 has an almost ideal chemical composition. The main difference between these two samples lays in the area between 150-300 cm-1. The one with a “cleaner” chemical composition has a separated, better developed doublet, while the one which contains Ba2+ has a less developed doublet, being almost a single broad peak. Both Raman bands have one strong peak in the area of 1050 - 1060 cm-1. Analogous with the Aragonite group, it is obvious that this strong peak is 2- characterised by V1 mode, precisely A1g (V1-symmetric C-O stretching of CO3 groups). The -1 small doublet in the area between 740 and 760 cm is the representation of V4 mode (Figure 20, Table 25).

Figure 20. Compiled and normalised RRUFF data on ancylite: R060218 (Source: Royal Ontario Museum M40089, Locality: Mont Saint-Hilaire, Rouville County, Quebec, Canada), R060205 (Source: Royal Ontario Museum M49550, Locality: Mont Saint-Hilaire, Rouville County, Quebec, Canada), R130005 (Source: Don Doell, Locality: Mont Saint-Hilaire, Rouville RCM, Monteregie, Quebec, Canada).

Table 26. Chemistry of the ancylite-(Ce) RRUFF samples. N Sample Chemistry Comments ID 3+ 1 R0602 (Ce0.40(La,Pr)0.23Ca0.18Nd0.10Sr0.09)Σ=1CO3((OH)0.67(H2O)0.2 Contains Pr

18 7F0.06)Σ=1 2+ 3+ 2 R0602 (Ce0.57La0.35Nd0.12Pr0.05)Σ=1.09(Ca0.44Sr0.36Ba0.04)Σ=0.84(CO Contains Ba and Pr

05 3)1.97(OH0.83F0.17)Σ=1.00·H2O 3 R1300 Unknown 05

5.2 Results

5.2.1 Anhydrous Carbonates

5.2.1.1 Anhydrous Carbonates with Simple Formula A + CO3

5.2.1.1.1 Calcite Group

5.2.1.1.1.1 Calcite

Figure 21. Calcite specimens in the mineralogical collection at the Department of Earth Sciences. Four calcite samples were chosen among 26 specimens at the mineralogical collection at the Department of Earth Sciences, shelf N39. The chosen samples differ in size and colour.

5.2.1.1.1.1.1 Calcite, sample 1

Figure 22. Calcite, sample 1. Observed physical properties: white coloured crystals, 2-3 cm long, form a flower-like intergrowth aggregate. There were five Raman spectra taken from the “rib” of crystals and from their sides (Figure 23, Table 26).

Figure 23. Five Raman spectra of the 1st calcite sample. Table 27. Raman peaks of the 1st calcite sample. External (cm-1) Internal (cm-1) Additional Combinational (cm-1) (cm-1)

Eg Eg Eg A1g Eg 2v2 148.6 – 276.8 – 711.4 – 1086.1 – Not 1. 1195.7 – Not identified

149.1 277.3 711.8 1086. 3 identified 1198.8 2. 1302.3 – 1302.8 3.1389.1 – 1389.6 4.1494.5 – 1495.9

Table 28. Full width at half maximum (FWHM) varies accordingly. External Internal Additional Combinational

Eg Eg Eg A1g Eg 2v2

18.5 – 19.7 – 21.1 9.1 – 12.5 6.5 – 7.0 47.8 – 1.97.9 – Not identified 21.0 94.6 122.7 2. 28.3 – 29.2 3. 32.3 – 66.3

5.2.1.1.1.1.2 Calcite, sample 2

Figure 24. Calcite, sample 2. Observed physical properties: 5-6 cm long transparent crystal of prismatic shape There were five Raman spectra taken, where two along c-axis, two perpendiculars the main axis and one at the angle of 110° in relation to the main axis (Figure 25)

Figure 25. Five Raman spectra of the 2nd calcite sample: along main axis, perpendicular to main axis and at the angle of 110° in relation to main axis. Table 29. Raman peaks of the 2nd calcite sample. External (cm-1) Internal (cm-1) Additional Combinational (cm-1) (cm-1)

Eg Eg Eg A1g Eg 2v2 147.7 – 276.0 – 710.5 – 1085.6 – Not 1. 1207.4 – Not identified 148.5 276.7 711.4 1085.9 identified 1214.7 2. 1302.0 – 1302.6 3. 1388.4 – 1391.3 4. 1492.7 5. 1524. 9 – 1552.2

Table 30. Full width at half maximum (FWHM) varies accordingly. External Internal Additional Combinational

Eg Eg Eg A1g Eg 2v2

15.0 – 16.5 – 21.5 7.9 – 11.1 5.8 – 6.3 56.2 (*) 1.21.5 – 23.3 Not identified

26.9 2.28.7 – 31.1 3. 32.5 – 36.2 4. 41.9 – 165.8

5.2.1.1.1.1.3 Calcite, sample 3

Figure 26. Calcite, sample 3. Observed physical properties: pink coloured fragment, 15 cm long There were five Raman spectra taken from this specimen (Figure 27)

Figure 27. Five Raman spectra of the 3rd calcite sample. Table 31. Raman peaks of the 3rd calcite sample. External (cm-1) Internal (cm-1) Additional Combinational (cm-1) (cm-1)

Eg Eg Eg A1g Eg 2v2 147.7 – 275.9 – 276. 710.6 – 1085.6 – 1434.1 – 1. 1301.0 – Not identified 147.8 1 711.0 1085.7 1453.4 1302.7 2. 1346.8 – 1347.1

Table 32. Full width at half maximum (FWHM) varies accordingly. External Internal Additional Combinational

Eg Eg Eg A1g Eg 2v2

15.7 – 16.6 – 16.8 8.3 – 8.7 6.0 – 6.2 3.1 – 9.0 1. 21.5 – Not identified 16.3 41.1 2. 4.3 – 5.0

5.2.1.1.1.1.4 Calcite, sample 4

Figure 28. Calcite, sample 4. Observed physical properties: 1-3 cm long transparent crystals with typical for calcite luster in an aggregate. There were five Raman spectra taken from this specimen (Figure 28)

Figure 29. Five Raman spectra of the 4th calcite sample. Table 33. Raman peaks of the 4th calcite sample. External (cm-1) Internal (cm-1) Additional Combinational (cm-1) (cm-1)

Eg Eg Eg A1g Eg 2v2 147.4 - 275.8 – 710.9 – 1085.6 1346.9 1.1301.9 – Not identified

147.6 276.0 711.0 1302.4 2. 1346.9

Table 34. Full width at half maximum (FWHM) varies accordingly. External Internal Additional Combinational

Eg Eg Eg A1g Eg 2v2

15.3 – 16.4 – 16.9 7.9 – 8.8 5.6 – 6.2 25.9 1.24.3 – 34.3 Not identified 16.0

In order to identify the nature of the additional peaks in the 1st and 2nd calcite samples, a comparison analysis was performed where the Raman spectra of both samples were compared to the RRUFF database. In this analysis, RRUFF samples with the most “contaminated” chemistry was chosen, more specifically R040070 and R040170 (Figure 30, Figure 31).

Figure 30. Comparison between the 1st calcite sample and RRUFF sample R040070.

Figure 31. Comparison between the 1st calcite sample and RRUFF sample R040170. The second sample was also compared to the RRUFF sample R050128. It has the ideal chemistry; however, it is a pseudomorph after aragonite, and is not represented by a single crystal. Besides, it still contains trace of aragonite (Figure 32).

Figure 32. Comparison between the 2nd calcite sample and RRUFF sample R050128. The third and the fourth samples were compared to the RRUFF samples with the ideal chemistry, R050127 and R050307 (Figure 33, Figure 34).

Figure 33. Comparison between the 3rd calcite sample and RRUFF sample R050127 (with ideal chemistry).

Figure 34. Comparison between the 4th calcite sample and RRUFF sample R050307 (with ideal chemistry).

5.2.1.1.1.2 Magnesite

Figure 35. Magnesite specimens. There were three magnesite samples chosen among 8 specimens at the mineralogical collection at the Department of Earth Sciences, shelf N 45. Chosen samples differ in size and colour. 5.2.1.1.1.2.1 Magnesite, sample 1

Figure 36. Magnesite, sample 1. Observed physical properties: cleavage fragment approximately 10 cm long, colour is white There were five Raman spectra taken from different sides of the fragment (Figure 37).

Figure 37. Five Raman spectra of the 1st magnesite sample. Table 35. Raman peaks of the 1st magnesite sample. External (cm-1) Internal (cm-1) Additional Combinational (cm-1) (cm-1)

Eg Eg Eg A1g Eg 2v2 205.3 – 325.2 – 735.2 – 1094.5 – Not Not Not identified 210.8 328.9 738.0 1095.3 identified identified

Table 36. Full width at half maximum (FWHM) varies accordingly. External Internal Additional Combinational

Eg Eg Eg A1g Eg 2v2

11.6 – 10.1 – 12.3 18.2 – 13.9 – Not Not Not identified 14.5 21.4 14.9 identified identified

5.2.1.1.1.2.2 Magnesite, sample 2

Figure 38. Magnesite, sample 2. Observed physical properties: white needles, 3-5 cm long in a grey matrix There were five Raman spectra taken from different sides of the fragment (Figure 39).

Figure 39. Five Raman spectra of the 2nd magnesite sample. Table 37. Raman peaks of the 2nd magnesite sample. External (cm-1) Internal (cm-1) Additional Combinational (cm-1) (cm-1)

Eg Eg Eg A1g Eg 2v2 Not 325.8 – Not 1094.4 – Not Not Not identified identified 327.6 identified 1096.1 identified identified

Table 38. Full width at half maximum (FWHM) varies accordingly. External Internal Additional Combinational

Eg Eg Eg A1g Eg 2v2

Not 9.4 – 11.4 Not 14.9 – Not Not Not identified identified identified 18.3 identified identified

5.2.1.1.1.2.3 Magnesite, sample 3

Figure 40. Magnesite, sample 3. Observed physical properties: 0.5 cm long crystals along veins in a weathered yellow matrix There were five Raman spectra taken from different sides of the fragment (Figure 41).

Figure 41. Five Raman spectra of the 3rd magnesite sample. Table 39. Raman peaks of the 3rd magnesite sample.

External (cm-1) Internal (cm-1) Additional Combinational (cm-1) (cm-1)

Eg Eg Eg A1g Eg 2v2 Not 294.5 – Not 1097.5 – Not 1. 167.7 – Not identified identified 297.6 identified 1098.0 identified 173.1 2. 1209.1 – 1209.5 3. 1268.1 – 1281.6

Table 40. Full width at half maximum (FWHM) varies accordingly. External Internal Additional Combinational

Eg Eg Eg A1g Eg 2v2

Not 15.2 – 17.1 Not 8.1 – 8.6 Not 1. 14.0 – Not identified identified identified identified 18.4 2. 19.4 – 20.9 3. 25.8 – 110.5

The comparison analysis of the experimental Raman band and the RRUFF data base shows that the externa mode in the area between 0 and 500 cm-1 is shifted towards the lower numbers standard sample (325 – 294 = 31), while internal mode A1g is on the expected places (Figure 42):

Figure 42. Comparison between the experimental Raman band of the 3rd magnesite sample and the RRUFF sample R040114 (Source: University of Arizona Mineral Museum 7562, Locality: Snarum, Norway), sample contains Fe incorporated in the main lattice.

5.2.1.1.1.3 Siderite

Figure 43. Siderite specimens. There were three siderite samples chosen among 15 specimens at the mineralogical collection at the Department of Earth Sciences, shelf N 42. Chosen samples differ in size and colour.

5.2.1.1.1.3.1 Siderite, sample 1

Figure 44. Siderite, sample 1. Observed physical properties: brown coloured rhombohedral crystals, 0.5 – 1.5 cm long, in an aggregate. There were five Raman spectra taken from different sides of the fragment (Figure 45).

Figure 45. Five Raman spectra of the 1st siderite sample. Table 41. Raman peaks of the 1st siderite sample. External (cm-1) Internal (cm-1) Additional Combinational (cm-1) (cm-1)

Eg Eg Eg A1g 2v2 178.3 – 282.0 – 729.2 – 1085.1 – Not Not identified

179.6 282.5 732.4 1086.2 identified

Table 42. Full width at half maximum (FWHM) varies accordingly. External Internal Additional Combinational

Eg Eg Eg A1g 2v2

22.1 – 20.4 – 22.1 15.3 – 11.2 – Not Not identified 25.1 29.0 11.5 identified

The comparison analysis of the experimental Raman band and the RRUFF data base shows that both internal peaks are located at the expected wavenumbers (730 cm-1 and 1085 cm-1), standard sample standard however, the external modes are shifted (1Eg: 195 – 179 = 16 and 2Eg: 299 – 282sample = 17). The experimental band is compared with sample R040034, which has the most “contaminated” chemical composition, along with Fe and Mg, it contains cations of Ca2+ and Mn2+.

Figure 46. Comparison between the experimental Raman band of the 1st siderite sample and the RRUFF sample R040034 (Source: University of Arizona Mineral Museum 7584; Locality: Pribram, Czech Republic).

5.2.1.1.1.3.2 Siderite, sample 2

Figure 47. Siderite, sample 2. Observed physical properties: brown coloured rhombohedral cleavage fragment with weathered surface There were five Raman spectra taken from different sides of the fragment (Figure 48).

Figure 48. Five Raman spectra of the 2nd siderite sample. Table 43. Raman peaks of the 2nd siderite sample. External (cm-1) Internal (cm-1) Additional Combinational (cm-1) (cm-1)

Eg Eg Eg A1g 2v2 173.2 – 277.3 - 728.2 – 1085.0 – Not Not identified 178.4 280.0 733.7 1086.0 identified

Table 44. Full width at half maximum (FWHM) varies accordingly. External Internal Additional Combinational

Eg Eg Eg A1g 2v2

23.3 – 17.1 – 19.8 10.5 – 9.1 – 11.2 Not Not identified 27.5 34.1 identified

5.2.1.1.1.3.3 Siderite, sample 3

Figure 49. Siderite, sample 3, with galena in the yellow quartz-rich matrix. Observed physical properties: brown coloured rhombohedral cleavage fragment in a pale- yellow matrix, containing fragments of galena. There were five Raman spectra taken from different sides of the fragment (Figure 50).

Figure 50. Five Raman spectra of the 3rd siderite sample. Table 45. Raman peaks of the 3rd siderite sample. External (cm-1) Internal (cm-1) Additional Combinational (cm-1) (cm-1)

Eg Eg Eg A1g 2v2 174.2 – 276.6 – 727.9 – 1084.2 – 1. 412.3 – Not identified 176.0 278.6 734.5 1085.4 413.8

Table 46. Full width at half maximum (FWHM) varies accordingly. External Internal Additional Combinational

Eg Eg Eg A1g 2v2

21.4 – 19.0 – 19.7 5.7 – 35.1 10.4 – 1. 8.4 – 9.4 Not identified 29.6 11.1

5.2.1.1.1.4 Rhodochrosite There are two samples chosen among two specimens at the mineralogical collection at the Department of Earth Sciences, shelf N 46.

5.2.1.1.1.4.1 Rhodochrosite, sample 1

Figure 51. Rhodochrosite, sample 1. Observed physical properties: pink cleavage fragment, 10-15 cm long There were five Raman spectra taken from different sides of the fragment (Figure 52).

Figure 52. Five Raman spectra of the 1st rhodochrosite sample. Table 47. Raman peaks of the 1st rhodochrosite sample.

External (cm-1) Internal (cm-1) Additional Combinational (cm-1) (cm-1)

Eg Eg Eg A1g Eg 2v2 172.7 – 281.6 – 716.2 – 1083.8 – 1411.0 – 1. 1542.8 Not identified 176.8 284.1 717.7 1084.5 1413.9

Table 48. Full width at half maximum (FWHM) varies accordingly. External Internal Additional Combinational

Eg Eg Eg A1g Eg 2v2

14.4 – 15.5 – 20.1 8.4 – 11.4 7.1 – 8.5 10.2 – 1. 3.3 Not identified 17.6 14.4

5.2.1.1.1.4.2 Rhodochrosite, sample 2

Figure 53. Rhodochrosite, sample 2. Observed physical properties: pink cleavage fragment, 8 -10 cm long There were five Raman spectra taken from different sides of the fragment (Figure 54).

Figure 54. Five Raman spectra of the 2nd rhodochrosite sample. Table 49. Raman peaks of the 2nd rhodochrosite sample. External (cm-1) Internal (cm-1) Additional Combinational (cm-1) (cm-1)

Eg Eg Eg A1g Eg 2v2 175.1 – 283.8 – 717.6 - 1082.3 – 1413.0 – Not 1725.4 176.9 284.2 717.8 1085.4 1413.5 identified

Table 50. Full width at half maximum (FWHM) varies accordingly. External Internal Additional Combinational

Eg Eg Eg A1g Eg 2v2

14.1 – 15.2 – 16.1 8.0 – 8.3 6.8 – 7.1 9.6 – 10.4 Not 11.4 15.3 identified

5.2.1.1.2 Aragonite group

5.2.1.1.2.1 Aragonite

Figure 55. Aragonite specimens. There are five aragonite samples chosen among 10 specimens at the mineralogical collection at the Department of Earth Sciences, shelf N 40. Chosen samples differ in size, transparency and colour. However, three of them did not give any Raman signals due to weathered surface and were discarded from the experiment.

5.2.1.1.2.1.1 Aragonite, sample 1

Figure 56. Aragonite, sample 1. Observed physical properties: coral-like fragment, 5-8 cm long There were five Raman spectra taken from different sides of the fragment (Figure 57).

Figure 57. Five Raman spectra of the 1st aragonite sample. Table 51. Raman peaks and FWHM of the 1st aragonite sample. Assignment Measurements (cm-1) FWHM

T(M,CO3) 147.3 – 147.8 (Ag) 15.6 – 16.2

External modes 275.4 – 276.3 (B3g) 16.5 – 17.6

ν4 Ag No No

B2g No No

B1g 711.1 – 711.3 8.4 - 8.8

B3g No No

ν2 Ag No No

B2g No No

ν1 Ag 1085.7 – 1085.8 5.5 – 6.2

B2g No No

ν3 B1g No No

B2g No No

Ag 1434.1 – 1434.4 7.9 – 10.1

B3g No No

2ν1 No No

5.2.1.1.2.1.2 Aragonite, sample 2

Figure 58. Aragonite, sample 2. Observed physical properties: brownish-white, glassy, half transparent fragment, 10-15 cm long There were five Raman spectra taken from different sides of the fragment (Figure 59).

Figure 59. Five Raman spectra of the 2nd aragonite sample. The comparative analysis shows that the first Raman spectrum of the 2nd aragonite sample almost fully coincides with the RRUFF sample X050023, which, unfortunately, misses the detailed chemical composition (Figure 60). The main difference of these two Raman bands from the rest of the results lay in the area between 1200 and 1400 cm-1. There are two doublets located in this area. The first doublet has peaks at 1211.5 cm-1 and 1244.0 cm-1. The second doublet has peaks at 1311.0 cm-1 and 1337.4 cm-1.

Figure 60. Comparison analysis of the first Raman band of the 2nd aragonite sample and RRUFF sample X050023. Table 52. Raman peaks and FWHM of the 2nd aragonite sample.

Assignment Measurements (cm-1) FWHM

T(M,CO3) 145.1 – 145.5 (Ag) 15.0 – 16.1

External modes 200.3 – 201.1 (B2g) 13.4 – 14.8

ν4 Ag 703.2 – 703.6 7.9 – 9.5

B2g No No

B1g No No

B3g No No

ν2 Ag No No

B2g No No

ν1 Ag 1084.6 – 1084.8 5.6 – 5.8

B2g No No

ν3 B1g No No

B2g No No

Ag No No

B3g No No

2ν1 No No

5.2.1.1.2.2 Cerussite

Figure 61. Cerussite sample. Observed physical properties: white – pale brown fragment of an aggregate which consists of tabular minerals, 1-5 cm long. This fragment of the cerussite was borrowed from the

72 mineralogical collection of the National Museum of the Natural History in Stockholm. There were five Raman spectra taken from different sides of the fragment (Figure 62).

Figure 62. Five Raman spectra of the cerussite sample. Table 53. Raman peaks and FWHM of the cerussite sample.

Assignment Measurements (cm-1) FWHM

T(M,CO3) 142.3 – 143.8 13.9 – 18.5 External modes 169.9 – 172.6 12.0 – 15.1 355.3 – 356.6 35.7 – 44.2

ν4 Ag No No

B2g 678.2 – 681.3 5.6 – 19.0

B1g No No

B3g No No

ν2 Ag 836.9 – 837.6 7.3 – 7.6

B2g No No

ν1 Ag 1053.2 – 1053.9 5.8 – 6.1

B2g 1253.5 – 1254.7 23.7 – 33.0

ν3 B1g No No

B2g No No

Ag No No

B3g 1659.7 – 1661.1 30.8 – 39.0

2ν1 1864.2 – 1865.3 33.3 – 37.0

5.2.1.1.2.3 Witherite

Figure 63. Witherite sample. Observed physical properties: small, 0.3 – 1.0 cm long white, half transparent minerals in an aggregate. This fragment of the cerussite was borrowed from the mineralogical collection of the National Museum of the Natural History in Stockholm. There were five Raman spectra taken from different sides of the fragment (Figure 64).

Figure 64. Five Raman spectra of the witherite sample. Table 54. Raman peaks and FWHM of the witherite sample.

Assignment Measurements (cm-1) FWHM

T(M,CO3) 127.6 – 128.5 (doublet) 13.4 – 15.6 External modes 147.9 – 149.6 12.7 – 14.8 216.2 – 217.5 18.1 – 20.3

ν4 Ag 689.1 – 689.4 8.1 – 8.4

B2g No No

B1g No No

B3g No No

ν2 Ag No No

B2g No No

ν1 Ag 1058.9 – 1059.1 4.9 – 5.7

B2g No No

ν3 combinational 1346.8 5.2 – 5.9

Ag 1418.7 – 1419.4 5.0 – 8.6

B1g No No

B2g No No

B3g No No

2ν1 No No

5.2.1.2 Anhydrous Carbonates with Compound Formula A + B ++ (CO3)2

5.2.1.2.1 Dolomite group

5.2.1.2.1.1 Dolomite

Figure 65. Dolomite specimens.

There are four dolomite samples chosen among 11 specimens at the Mineralogical Collection at the Department of Earth Sciences, shelf N 41. Chosen samples differ in size, transparency and colour. 5.2.1.2.1.1.1 Dolomite, sample 1

Figure 66. Dolomite, sample 1. Observed physical properties: a white-grey fragment with zones of precipitated mineral, which has golden-metallic colouring and cubic crystallographic structure. We assume that the second mineral is pyrite. There were five Raman spectra taken from different sides of the fragment. The most representative Raman bands were used for the comparative analysis with RRUFF sample of dolomite and RRUFF sample of pyrite in order to evaluate the “finger print” of the pyrite on the tested 1st dolomite sample (Figure 67).

Figure 67. The comparative analysis between Raman spectrum of the 1st dolomite sample and RRUFF sample of dolomite, along with RRUFF sample of pyrite. Table 55. Raman peaks and FWHM of the 1st dolomite sample. Measurements (cm-1) FWHM Assignment

169.1 – 169.6 14.1 – 14.4 T(Ca, Mg, CO3)

295.1 – 295.7 15.2 – 16.6 T(Ca, Mg, CO3)

345.1 – 345.2 12.6 15.0 Additional (pyrite “finger print”)

724.0 – 724.8 12.7 – 15.1 V4- Symmetric CO3 deformation

No No V2- Asymmetric CO3 deformation 1097.7 - 1097.8 7.8 – 8.4 V1- Symmetric CO3 stretching 1440.7 – 1441.1 7.2 – 10.7

1762.9 4.2 V3- Asymmetric CO3 stretching No No No No V1 + V4

2V2 + V4

2V3

5.2.1.2.1.1.2 Dolomite, sample 2

Figure 68. Dolomite, sample 2. Observed physical properties: fragment, 10-15 cm long, coloured in tan-grey. There were five Raman spectra taken from different sides of the fragment (Figure 69).

Figure 69. Five Raman spectra of the 2nd dolomite sample. Table 56. Raman peaks and FWHM of the 2nd dolomite sample. Measurements (cm-1) FWHM Assignment

167.8 – 168.5 14.1 – 14.8 T(Ca, Mg, CO3)

293.6 – 294.0 16.2 – 18.1 T(Ca, Mg, CO3)

723.9 – 727.3 11.2 – 35.6 V4- Symmetric CO3 deformation

No No V2- Asymmetric CO3 deformation 1096.9 – 1097.1 8.8 – 8.9 V1- Symmetric CO3 stretching 1440.2 3.0

No No V3- Asymmetric CO3 stretching, very No No weak

No No V1 + V4

2V2 + V4

2V3

5.2.1.2.1.1.3 Dolomite, sample 3

Figure 70. Dolomite, sample 3. Observed physical properties: fragment, 15-20 cm long, red coloured, weathered surface There were five Raman spectra taken from different sides of the fragment (Figure 71).

Figure 71. Five Raman spectra of the 3rd dolomite sample.

Table 57. Raman peaks and FWHM of the 3rd dolomite sample. Measurements (cm-1) FWHM Assignment

168.6 – 169.5 14.1 – 14.7 T(Ca, Mg, CO3)

294.8 – 295.0 15.4 – 16.7 T(Ca, Mg, CO3)

410.0 – 411.9 13.5 – 36.0 Additional

724.0 – 724.3 12.5 – 14.6 V4- Symmetric CO3 deformation

No No V2- Asymmetric CO3 deformation 1097.3 – 1097.5 8.3 – 8.5 V1- Symmetric CO3 stretching 1440.4 – 1441.6 7.1 – 9.2

No No V3- Asymmetric CO3 stretching

No No V1 + V4 No No 2V2 + V4

2V3

5.2.1.2.1.1.4 Dolomite, sample 4

Figure 72. Dolomite, sample 4. Observed physical properties: white-grey fragment in the dark matrix. There were five Raman spectra taken from different sides of the fragment (Figure 73). The matrix did not give any readable signals and, thus, was discarded from the analysis.

Figure 73. Five Raman spectra of the 4th dolomite sample. Table 58. Raman peaks and FWHM of the 4th dolomite sample. Measurements (cm-1) FWHM Assignment

453.0 – 455.0 16.7 – 18.8 T, L external

614.9 – 615.4 9.8 – 11.7 T, L external (doublet)

645.0 – 645.3 8.1 – 10.0 Internal modes:

987.0 6.0 – 6.8 ν1 (PO4)3- symmetric stretching modes 1139.1 – 1140.4 12.9 – 14.2

1165.1 – 1165.7 9.8 – 12.8 ν3 (PO4)3- antisymmetric stretching modes.

“doublet” of V3

The Raman band of sample 4 differs from the dolomite Raman band significantly. The Crystal Sleuth RRUFF search engine gave only 14% match with dolomite. In order to identify the real nature of the tested mineral, the comparative analysis with RRUFF data base was performed. The RRUFF sample R060192 was chosen for the comparative analysis (Figure 74). However, the result differes significant from the apatite’s Raman band (Figure 74). The tested mineral proved to be dolomite with significantly shifted peaks (Figure 73).

Figure 74. The comparative analysis between sample 4 and the RRUFF sample, R060192 (Source: Luiz Menezes; Locality: Parelhas, Rio Grande de Norte, Brazil).

5.2.1.3 Anhydrous Carbonates with Compound Formula A+2 B++2 (CO3)4

5.2.1.3.1 Burbankite Group (Hexagonal)

5.2.1.3.1.1 Burbankite

Figure 75. Burbankite sample. Observed physical properties: white - greyish yellow fragment, 5-6 cm long. This fragment was borrowed from the mineralogical collection of the National Museum of the Natural History in Stockholm. It was decided to take 12 Raman bands in order to register burbankite’s more complex chemistry (as compared to previous carbonates) and structure (Figure 76 - 77). There are two main types of the burbankite’s Raman bands: the first one has the strongest peak with a

82 shoulder (Figure 76 - 77: 1,3,4,6,7-12) and the second one has a well-developed split of the same peak, creating a well-defined doublet (2 and 5). The fist type occurs more often, in 73% of cases of in this study.

Figure 76. First six (1-6) Raman spectra of the burbankite sample.

Figure 77. Second six (7-12) Raman spectra of the burbankite sample. Table 59. Raman peaks and FWHM of the burbankite sample. Measurements (cm-1) FWHM Assignment 148.7 – 151.4 14.7 – 19.5 External mode 205.5 – 209.5 36.2 – 47.6 276.7 – 295.7 14.1 – 49.8 551.9 4.4 Additional 609.3 4.7 Additional Internal mode:

712.1 – 724.1 8.2 – 12.6 V4 Ag

1086.5 – 1199.6 5.6 – 9.1 V2 1241.6 – 1246.6 32.8 – 49.0 Strong fluorescence

1606.6 – 1613.3 34.3 – 64.3 Strong fluorescence

The second type of the burbankite’s Raman band has the double, which has peaks at 1226- 1234 cm-1 and at 1262-1280 cm-1. The second important distinction of the second type is the absence of V4 Ag and V2 Ag. The strongest peaks (both the single peak with the shoulder and the doublet) are the result of the fluorescence.

5.2.1.4 Carbonates - Hydroxyl or Halogen (I)

5.2.1.4.1 Carbonates - Hydroxyl or Halogen where (A B)2 (XO3) Zq

5.2.1.4.1.1 Malachite Group

5.2.1.4.1.1.1 Malachite Cu2CO3(OH)2

Figure 78. Malachite specimens. There are three malachite samples chosen among 20 specimens at the mineralogical collection at the Department of Earth Sciences, shelf N 43. Chosen samples differ in size and colour. The rest of the samples did not give readable signals and, threrefore, were discarded from the experiment. Weathered, partly destroyed surface is the probable reason for poor signals’ quality. 5.2.1.4.1.1.1.1 Malachite, sample 1

Figure 79. Malachite, sample 1. Observed physical properties: fragment of a rock, 5-8 cm long, most probably limestone (rusted yellow-white) with precipitated malachite (green) on the surface. There were five Raman spectra taken from different sides of the fragment (Figure 80).

Figure 80. Five Raman spectra of the 1st malachite sample. The results differ so significantly from the RRUFF data base, that it is ligitimate to state that they are not Raman bands of malachite. We assume that our results depict the host rock, calcite/aragonite. We believe that these Raman spectra show the polycrystalline quartz occurring in the veins of the calcite. In order to prove or discard this hypothesis, we perform the comparative analysis with one of the RRUFF quartz samples, R150074, of natural occurrence (Figure 81).

Figure 81. Comparison analysis beween the 1st malachite sample and RRUFF sample of quartz, R150074 (Source: UAMM 9180, Locality: Selvino, Bergamo, Italy). Table 60. Raman peaks and FWHM of the 1st malachite sample.

Measurements (cm-1) FWHM Assignment

122.9 – 123.2 12.9 – 14.0 T(SiO2) Quartz external mode

199.6 – 201.5 28.2 – 32.2 ν4-Symmetric SiO2 bending mode

260.1 – 263.4 15.0 – 27.8 Additional (T(Cu, CO3)) Malachite external mode 352.8 – 354.7 5.6 – 16.6 ν2-Asymmetric SiO2 bending mode

396.1 – 396.8 12.8 – 24.9 Additional (T(Cu, CO3)) Malachite external mode

462.2 – 462.5 12.9 – 13.6 ν1-Symmetric SiO2 stretching mode

No No ν3-Asymmetric SiO2 stretching mode

5.2.1.4.1.1.1.2 Malachite, sample 2

Figure 82. Malachite, sample 2. Observed physical properties: fragment of a rock, 5-6 cm long, most probably limestone (rusted yellow-white) with precipitated malachite (green) on the surface. There were five Raman spectra taken from different sides of the fragment (Figure 83).

Figure 83. Three Raman spectra of the 2nd malachite sample and two Raman spectra of the host rock. In this case the results differ also significantly from the RRUFF data base, therefore, we believe that they are also not Raman bands of malachite. We assume that we have the similar situation as with the 1st malachite sample and, thus, we perform the comparative analysis with one of the RRUFF quartz samples, R150074, of natural occurrence (Figure 84).

Figure 84. Comparison analysis beween the 2nd malachite sample and RRUFF sample of quartz, R150074 (Source: UAMM 9180, Locality: Selvino, Bergamo, Italy). Table 61. Raman peaks and FWHM for the 2nd malachite sample. Measurements (cm-1) FWHM Assignment

122.9 – 123.6 12.5 – 14.0 T(SiO2)

201.7 – 202.7 24.8 – 33.0 ν4-Symmetric SiO2 bending mode

261.3 – 262.7 8.5 – 13.2 Additional (T(Cu, CO3)) Malachite external mode. *Applies only for the mineral’s Raman spectrum, not for the matrix. 351.5 – 353.5 13.2 – 18.7 ν2-Asymmetric SiO2 bending mode

399.5 – 400.6 5.1 – 22.5 Additional (T(Cu, CO3)) Malachite external mode. *Applies only for the mineral’s Raman spectrum, not for the matrix. 462.5 – 462.7 12.6 – 13.0 ν1-Symmetric SiO2 stretching mode

No No ν3-Asymmetric SiO2 stretching mode

5.2.1.4.1.1.1.3 Malachite, sample 3

Figure 85. Malachite, sample 3. Observed physical properties: fragment of a rock, 5-6 cm long, fully covered by a thin layer of malachite (green). The host rock is accessible and visible at the rock’s sides and edges. There were five Raman spectra taken from different sides of the fragment (Figure 86).

Figure 86. Four Raman spectra of the 3rd malachite sample and two Raman spectrum depict the host rock. Table 62. Raman peaks and FWHM of the 3rd malachite sample. Measurements (cm-1) FWHM Assignment

275.5 – 275.9 5.6 – 35.4 T(Cu, CO3) 287.5 – 291.1 4.5 – 16.7

No No ν4-Symmetric CO3 bending mode

987.3 – 987.9 11.8 – 12.1 ν2-Asymmetric CO3 bending mode

1086.1 – 1160.2 2.8 – 7.1 ν1-Symmetric CO3 stretching mode

1270.1 – 1275.6 2.1 – 34.6 Additional 1325.7 – 1328.4 1.2 – 3.4 ν3-Asymmetric CO3 stretching mode 1466.9 – 1467.0 4.1 – 6.6

No No O-H bending mode

No No O-H stretching mode

Table 63. Raman peaks and FWHM of the host rock. Measurements (cm-1) FWHM Assignment

150.7 – 151.0 14.9 – 15.1 T(Cu, CO3)

277.9 – 278.0 16.3 ν4-Symmetric CO3 bending mode

711.5 – 711.6 8.1 – 8.3 ν2-Asymmetric CO3 bending mode

1086.2 – 1086.3 6.1 ν1-Symmetric CO3 stretching mode

1435.1 8.0 ν3-Asymmetric CO3 stretching mode

Figure 87. Comparison between the 3rd malachite sample and RRUFF malachite, ID 050508.

5.2.1.5 Carbonates - Hydroxyl or Halogen (II)

5.2.1.5.1 Carbonates - Hydroxyl or Halogen where (A)m (B)n (XO3)p Zq, with (m+n):p=1:1

5.2.1.5.1.1 Ancylite group

5.2.1.5.1.1.1 Ancylite-(Ce) SrCe(CO3)2(OH)•(H2O)/ ancylite-(La) Sr(La,Ce)(CO3)2(OH)•(H2O)

Figure 88. Ancylite sample. Observed physical properties: fragment, 4-5 cm long, aggregate of 0.3-0.5 cm long milk- white crystals. Edges are rusted yellow, denuding a host rock. This fragment was borrowed from the mineralogical collection of the National Museum of the Natural History in Stockholm. There were five Raman spectra taken in total (Figure 89).

Figure 89. Five Raman bands of the ancylite. There are a few distinctions in the Raman bands of the tested ancylite. In order to identify them, we perform the comparative analysis with the RRUFF data base (Figure 90). It shows that two peaks of the external modes in the area between 167 cm-1 and 295 cm-1 don’t build a single peak with a shoulder nor a doublet as RRUFF sample, R060205, does. It demonstrates that V2-assymetric CO3 bending mode doesn’t build a doublet, as RRUFF sample, but creates a single peak at 723 cm-1. But the most significant distinction is a presence of a doublet at

1242 cm-1 with a shoulder (almost undeveloped triple), which indicates presence of strong fluorescence.

Figure 90. Comparison between the tested ancylite ad the RRUFF sample R060205 (Source: Royal Ontario Museum M49550, Locality: Mont Saint-Hilaire, Rouville County, Quebec, Canada). Table 64. Raman peaks and FWHM of the ancylite sample. Measurements (cm-1) FWHM Assignment

167.8 – 168.6 14.1 – 17.2 T(Cu, CO3)

293.4 – 295.5 15.7 – 19.1 ν4-Symmetric CO3 bending mode

722.9 – 723.3 13.4 – 13.9 ν2-Asymmetric CO3 bending mode

1096.6 – 1096.9 8.4 – 9.0 ν1-Symmetric CO3 stretching mode

1196.6 – 1200.3 13.2 – 20.3 Additional, fluorescence

1241.8 – 1242.0 34.0 – 40.3 1290.6 – 1295.0 21.7 – 39.3 1492.9 8.0 ν3-Asymmetric CO3 stretching mode

5.3 Discussion

5.3.1 Anhydrous Carbonates

5.3.1.1 Anhydrous Carbonates with Simple Formula A + CO3

5.3.1.1.1 Calcite Group

5.3.1.1.1.1 Calcite Four calcite samples were studied with Raman spectroscopy and 20 Raman spectra were taken in total. The comparison analysis with the RRUFF database showed that the third and the fourth samples have the most ideal chemistry. They have no detected shifts, having in total five modes (the 3rd sample) and four modes (the 4th sample). However, both samples’ spectra contain additional peaks at 1301 and 1346 cm-1, respectively. -1 The weak Raman peak at 1301 cm represents the CH2 twisting vibration (Lobo & Bonilla,

2003). CH2, methylene, is an organic compound. This organic compound could be absorbed by the calcite. Thomas et al. (1993) reviewed in their studies that investigations about higher concentrations of organic compounds in the carbonate minerals, and specifically on fatty acids, is common in the mineral industry, where monolayer adsorption of fatty acids of the animal origin is used to float calcite. There can be a link between the presence of the organic matter in the carbonate rock, like calcite, and the presence of the oil/gas reservoir; however, this correlation is not fully confirmed. The second weak Raman band at 1346 cm-1 indicates the presence of graphite in the calcite (Kim et al., 2011). Graphite is the allotrope of carbon. Most probably a part of carbon presented in the calcite converted to graphite due to the changes in the pressure-temperature conditions. Graphite is associated with calcite and often forms in metamorphic rocks as a result of the reduction of sedimentary carbon compounds during metamorphism and can thus occur incorporated in the calcite crystal structure. The first and the second calcite samples showed a high concentration of impurities in the calcite structure. The comparison analysis with the RRUFF most “contaminated” samples did not give any results (Figure 30 and 31, Figure 32). However, the comparison analysis with RRUFF sample R050128 gave more similarities. RRUFF sample R050128 has ideal chemistry, however, it is a pseudomorph of aragonite, and still contains trace of aragonite (Figure 32). It is tempting to conclude that the first and the second calcite specimens also have traces of aragonite. However, this hypothesis is not proved by our analysis.

Apart from the additional peaks, which were discussed above, the first sample showed an additional peak at 1195 – 1198 cm-1. The presence of this peak can indicate the presence of calcium dipicolinate (Monoharan et al., 1990). Calcium dipicolinate is a chemical compound with 5-15% by dry weight of bacterial spores. It forms complex molecules, where calcium ions bond to the endospore core. I assume that the calcium dipicoline could be formed during calcite crystallization from limestone, which contained shells from dead marine organisms, as well as bacterial spores. Most probably not all material of the organic origin was converted into limestone before it crystallised into calcite. There was presumably some organic material left, which was rapidly converted to calcite, believably due to a metamorphism event. Except for the additional peaks which were discussed above, the second sample showed an additional peak at 1207 – 1214 cm-1. The nature of this impurity is poorly understood. One hypothesis is the bending of CH2. However, it is not proved by literature.

5.3.1.1.1.2 Magnesite Three magnesite samples were studied with Raman spectroscopy and 15 Raman spectra were taken in total. The 1st and the 2nd magnesite samples show expected results. However, the -1 internal mode Eg at 1445 cm and combinational 2v2 are missing in both Raman bands; -1 sample 2 misses the external mode Eg at 212 cm . Perhaps, due to the orientation effect. Despite missing peaks, the most characteristic peaks at 325 cm-1 and at 1095 cm-1 are well defined and, thus, magnesite is recognisable by these Raman bands (they are located at 328 and at 1094 cm-1 in the literature). There are no significant distortions which would point to impurities or any other changes in the lattice of the mineral. -1 The third sample shows significant shifts. The external mode Eg at 328 cm is shifted -1 towards the lower numbers and is located at approximately 295 cm . The internal mode A1g, -1 -1 -1 which was expected at 1084 cm , is located at 1097 cm . This 13 cm shift of the V1 mode, 2- responsible for symmetric C-O stretching of CO3 groups, along with an external deviation can identify the lower Fe concentration compared to Mg. Spivak et al. (2014) demonstrated with her studies that modes are shifted to low wave numbers with an increasing Fe concentration in the MgCO3–FeCO3 solid solution of the magnesite-siderite series. Correspondingly, with higher concentration of Mg, the Raman peak positions shift to higher numbers, because Mg2+ ions have smaller radius and lighter mass than Fe2+ ions (Boulard et al., 2012). Raman spectroscopy registered also the presence of three additional peaks in the Raman band of the 3rd magnesite sample. The first one at approximately 170 cm-1 belongs to the

95 external extra modes. The two last ones at 1209 cm-1 and 1269 cm-1 are most probably the signals of organic impurities on the surface of the mineral.

5.3.1.1.1.3 Siderite Three siderite samples were studied with Raman spectroscopy and 15 Raman spectra were taken in total. The 1st siderite sample shows a significant shift in the external mode: 178 cm-1 instead of the expected 195 cm-1; and 282 cm-1 instead of the expected 299 cm-1. However, both internal modes are placed where they were expected to be: at 731 cm-1 and 1086 cm-1. We believe that the shift in the lattice mode indicates the higher ratio of Fe in relation to Mg, exactly as it is the case with the third maganasite sample. A similar situation is with the 2nd siderite sample, where the external mode is shifted towards the lower numbers from 195 cm-1 to 173-178 cm-1 and 299 cm-1 is shifted to 277-280 cm-1, while the internal modes are at the expected positions: at 728-733 cm-1 and at 1085- 1086 cm-1, respectively. The 3rd siderite sample is surrounded by a brown rusty matrix, which does not give any clear signal due to a surface destroyed by weathering. A fragment of galena is also incorporated into the rock. This specimen has exactly the same shift of the external mode: 195 cm-1 is shifted to 174-176 cm-1 and 299 cm-1 is shifted to 276-278 cm-1, while the internal peaks are at the expected positions: at 727-734 cm-1 and respectively at 1084-1085 cm-1. According to Spivak et al. (2014) and Boulard et al. (2012), shifted to the lower numbers peaks, indicate the high ratio of Fe in relation to Mg. All three samples showed this tendency.

5.3.1.1.1.4 Rhodochrosite The 1st rhodochrosite sample has an almost optimal Raman band, with two exceptions: the first extra mode’s peak is slightly shifted from 183 cm-1 to 175 cm-1 and the combinational st mode of 2V2 is not registered. Despite these deviations, the Raman band of the 1 rhodochrosite sample is an example of a clean chemical composition, free from impurities. The 2nd rhodochrosite sample has an absolutely optimal Raman band. It has also a lightly shifted external mode peak from 183 cm-1 to 175 cm-1. However, the Raman band of this sample has even a combinational mode at 1725 cm-1. Full width at half maximum (FWHM) is small for both samples and varies between 8 and 15 for all peaks. The measurements of both samples coincide almost fully with RRUFF data for samples with a clean chemical composition, like the R050019.

5.3.1.1.2 Aragonite group

5.3.1.1.2.1 Aragonite

st The Raman band of the 1 aragonite sample shows five characteristic peaks: two external (Ag and B3g) and three internal (V4 B1g, V1 Ag, and V3 Ag). Almost all peaks are located at their expected positions: 148 cm-1 (expected 142 cm-1), 276 cm-1 (expected between 250 – 285 cm- 1), 1085 cm -1 (expected 1083 – 1085 cm-1). The only exception is the peak, which is located at 711 cm-1 instead of the expected 701 cm-1. The expected accuracy of the system is 1-2 wavenumbers. The portable Raman spectroscopy failed to register V3 and the combinational

2V1. The Raman band of the 2nd aragonite sample shows only four characteristic peaks: two external (Ag and B2g) and two internal (V4 Ag and V1 Ag). Our method did not detect V2, V3 -1 and combinational 2V1. The external mode, B2g, showed a significant shift: 201 cm instead of expected 250 – 285 cm-1. But despite the failure to register some internal modes, aragonite is recognisable on both Raman bands. Comparative analysis with RRUFF data base shows that one Raman band of RRUFF sample X050023 coincides with the 1st Raman band of the 2nd aragonite sample. Unfortunately, a detailed chemical analysis of the RRUFF sample was not performed. Most probably, both the RRUFF sample and the 2nd aragonite sample contain additional chemical elements, which give contamination bands in the area between 1200 and 1400 cm-1 and shifted external B2g.

5.3.1.1.2.2 Cerussite The Raman band of the cerussite shows ten characteristic peaks: three external and seven internal. This result exceeds even some results in the literature. The Raman spectrum is detailed and has enough peaks to reliably identify the cerussite: external peaks (142-143, 169- -1 -1 -1 172 and 355-356 cm ), internal peaks (V4 Ag at 678-681 cm ; V2 Ag at 836-837 cm ; V1 Ag -1 -1 -1 at 1053 cm and B2g at 1253 – 1254 cm ; v3 B1g at 1332 – 1333 cm and B3g at 1659 – 1661 -1 -1 cm ) and even the rare-to-register combinational peak 2V1 at 1864-1865 cm . However, some peaks have large FWHM, e.g. V1 B2g has FWHM between 23.7 – 33.0. This means that this result can be improved in order to increase the resolution of the peaks. The Raman band does not show any deviations from the literature within 142 and 1253 cm- 1. It allows us to conclude that the cerussite has an almost ideal chemical composition, free from impurities. The peak at 1332 cm-1 is due to the fluorescence effect and is, perhaps, linked with the presence of REE.

5.3.1.1.2.3 Witherite One witherite sample was studied with Raman spectroscopy and 5 Raman spectra were taken in total. The Raman band shows the characteristic doublet in the area between 127 cm-1 and -1 150 cm , which is responsible for the external mode. There were three internal modes, V4, V1 and V3, identified during the experiment. The strongest and the most characteristic peak, 2- responsible for V1-symmetric C-O stretching of CO3 groups, is located at the expected -1 position, at 1059 cm . Two internal modes, V3 and combinational 2V1, were not identified. FWHM, full width at half maximum, varies, being narrow in the area of the internal modes and expanding in the area of the external peaks. The situation is similar with the RRUFF witherite samples, where internal peaks are sharper, while external are broader. The Raman spectroscopy did not identify any deviations or external peaks. The witherite sample has a close-to-ideal chemical composition, free from impurities.

5.3.1.2 Anhydrous Carbonates with Compound Formula A + B ++ (CO3)2

5.3.1.2.1 Dolomite group

5.3.1.2.1.1 Dolomite The 1st dolomite sample proved to have a “finger print” from the precipitated pyrite in its

Raman band. The most characteristic V1-peak, responsible for the symmetric CO3 stretching, is located in the expected place at 1098 cm-1. However, the shift of the external mode – 187 cm-1 is shifted to 169 cm-1 and 309 cm-1 is shifted to 295 cm-1 – along with the additional peak at 345 cm-1 points to the influence of the pyrite’s presence. The Raman band of the 1st dolomite sample is mixed, representing peaks from both dolomite and pyrite. The 2nd dolomite sample has also a slightly shifted external mode: 187 cm-1 is shifted to -1 -1 168 cm . The main peaks, V1 and V4, are located in the expected places: 1097 and 725 cm . Despite, the shift of the external mode, there is no signal of the presence of another mineral. The shift is caused most probably by an impurity. The 3rd dolomite sample has a shifted external mode: 187 cm-1 is shifted to 169 cm-1, and contains an additional peak at 411 cm-1. Both facts indicate that this sample contains impurities. Though the sample 4 has significantly shifted peaks, we believe that it is dolomite. We assume that this sample contains impurities which are responsible for the shift. The comparative analysis with the apatite did not show the match.

The experiment with dolomite shows that the presence of another mineral or impurities influence the external modes as the most, while the internal peaks (within 725 and 1097 cm-1) stay almost unchanged.

5.3.1.3 Anhydrous Carbonates with Compound Formula A+2 B++2 (CO3)4

5.3.1.3.1 Burbankite Group (Hexagonal)

5.3.1.3.1.1 Burbankite One burbankite sample was studied with Raman spectroscopy and 12 Raman spectra were taken in total. The collected Raman bands showed to differ significantly from the RRUFF samples. There are only three RRUFF Raman bands of burbankite and the information in the literature is scarce. We found that there are two main types of burbankite Raman bands: the first one has fluorescence peak with a shoulder, and the second one has a well-developed split of the same peak, creating a well-defined doublet. The common features between our results and the RRUFF samples are the positions of two peaks (V2 and V4). The strong fluorescence has broad FWHM (full width at half maximum) between 32.8 – 49.0. We believe that the two different REEs create two different types of the fluorescence bands. Burbankite has a complex chemical composition and crystallographic structure. Therefore, it requires a more detailed examination of the Raman spectroscopic signals. The chemical complexity gives rise to several fluorescence band types, two of which we managed to identify.

5.3.2 Carbonates - Hydroxyl or Halogen (I)

5.3.2.1 Carbonates - Hydroxyl or Halogen where (A B)2 (XO3) Zq

5.3.2.1.1 Malachite Group

5.3.2.1.1.1 Malachite Three malachite samples were studied with the help of the Raman spectroscopy. The first sample showed a very strong fingerprint of the host rock, calcite. The comparative analysis showed that our results fully coincide with quartz Raman spectra, with the strongest peak at -1 462 cm representing V1, symmetric SiO2 stretching mode. There are two additional peaks at 262 cm-1 and 398 cm-1 that point to the presence of malachite. Both peaks are the result of the translational movement of the lattice of malachite. In summary, the 1st malachite sample

99 showed a quartz Raman spectrum with a strong background signal, the host rock, with two additional peaks belonging to the external modes of malachite. The second malachite sample showed almost exactly the same result. There were five Raman bands taken in total: three bands from the malachite and two from the host rock. The results of the host rock pointed to calcite with a high quartz quantity. The Raman bands of the malachite coincided fully with the quartz Raman spectrum, except for two additional peaks at 262 cm-1 and 400 cm-1. These two additional peaks belong to the malachite external modes. The third sample showed the closest to the malachite Raman signal among all specimens. In the case of sample 3, it was possible to separate the host rock, calcite, from the malachite -1 signal. The host rock had the strongest peak at 1086 cm , V1, symmetric CO3 stretching mode -1 and V2-assymetric CO3 bending mode at 711 cm . Both peaks are characteristic for calcite. The results of Raman spectroscopy of the malachite clearly showed two external modes at -1 -1 -1 -1 - 275 cm and 290 cm and 5 internal modes: V2 at 987 cm , V3 at 1326 cm and at 1466 cm 1. All peaks are characteristic for malachite. In summary, only the 3rd malachite sample gave a kind of Raman signals, characteristic for malachite. The signal of the host rock, calcite, could be separated from the Raman band of the mineral. The 1st and 2nd samples showed a strong overprint of the background of the host rock, calcite, with high quantity of quartz. The acquisition time for the malachite samples was 10 x 10 = 100 seconds (1 min 40 seconds), but, perhaps, even longer acquisition time was required to register the malachite Raman signature.

5.3.2.2 Carbonates - Hydroxyl or Halogen (II)

5.3.2.2.1 Carbonates - Hydroxyl or Halogen where (A)m (B)n (XO3)p Zq, with (m+n):p=1:1

5.3.2.2.1.1 Ancylite group 5.3.2.2.1.1.1 Ancylite-(Ce) SrCe(CO3)2(OH)•(H2O)/ ancylite-(La) Sr(La,Ce)(CO3)2(OH)•(H2O) We studied a fragment of ancylite with the help of Raman spectroscopy and took five Raman bands in total. Our results differed from the RRUFF database. Two peaks of the external modes in the area between 167 cm-1 and 295 cm-1 didn’t show a single peak with a shoulder, nor a doublet, as the RRUFF samples do. The internal mode, V2-assymetric CO3 bending mode, also didn’t build a doublet, as the RRUFF sample does, but created a single peak at 723 cm-1 instead. A significant distinction was the presence of a doublet at 1242 cm-1 with a shoulder – an almost undeveloped triple. Despite these differences, the most characteristic

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-1 peak, V1, was in the expected place at 1097 cm . Thus, we can state that our tested ancylite has readable and recognisable Raman signals. The chemical composition and the crystallographic structure of the ancylite is complex. We believe that the additional doublet in the area of the internal modes (within 1196 and 1295 cm -1) reveals presence of impurities, most probably the presence of other rare earth metals. In order to prove or discard this hypothesis, a detailed chemical analysis should be performed. However, the deviations of the external modes most probably indicate imposed signals from the host rock, which, according to the peaks’ positions, is likely to be calcite.

5.4 Conclusions There are 11 carbonate minerals studied by the Raman spectroscopy in total. Four minerals belong to the Calcite group, three minerals are from the Aragonite group. There are also the Dolomite, Burbankite, Malachite and Ancylite groups. The most characteristic features of the Calcite group are the following. The strongest -1 -1 internal peak, V1 Ag, at 1085 cm for calcite, siderite and rhodochrosite and at 1095 cm for -1 -1 magnesite. The second typical peak, V3, varies from 712 cm for calcite to 735 cm for magnesite. There are five characteristic peaks for the whole Calcite group: two external and three internal, except for siderite, which has four peaks, where two peaks are external and two 2- are internal modes. All peaks are characterised by the motion of the CO3 group, all deviations come from the difference in size and weight of the metal cations. For example, Mg2+ is smaller than Ca2+ and, therefore, the main peaks of magnesite are shifted towards higher wavenumbers. The knowledge about this difference can help to identify the chemical ratio of Fe in relation to Mg. The Aragonite group has seven characteristic modes: two external, four internal and one combinational. However, the portable Raman system detected all seven bands only for cerussite, failing to register V2 and the combinational one for aragonite and witherite. The -1 most characteristic peak, V1 Ag, is located at 1085 cm for aragonite, which is the high- pressure polymorph of calcite; at 1053 cm-1 for cerussite and at 1059 cm-1 for witherite. The difference in the location of the main peak depends on the metal cations’ size and weight. Aragonite’s cation is calcium. Calcium has a van der Waalsradius of 240 pm, while the cerussite’s cation, lead, has a van der Waalsradius of 180 pm and the witherite’s cation, barium, has the largest van der Waalsradius of 270 pm. For example, the strongest internal -1 -1 mode Ag for aragonite is located at 1085 cm , while for cerussite - at 1054 cm and for witherite - at 1060 cm-1. However, the linear relationship between the cation’s size and the

101 shift in wavenumbers of the Calcite group does not apply to the Aragonite group. The size difference gives different shifts, but it is not necessarily the case when the smallest cation gives the shift towards the higher wavenumbers. The reason for the Aragonite group not following the Calcite size–shift correlation is in the crystallographic difference: calcite has a trigonal system, while aragonite has an orthorhombic system. -1 The strongest peak, V1 Ag, of dolomite is located at 1097 cm . Dolomite contains two cations, calcium and magnesium, spread in the mineral lattice, together giving the shift towards higher wavenumbers. We observed the influence of the presence of another mineral on the dolomite’s Raman spectrum, i.a. the fingerprint of pyrite. Burbankite has a complex chemical composition, containing at least five different cations: Na, Ca, Sr, Ba, Ce. We identified two different types of Raman spectra, which are characteristic for burbankite. However, we assume that there is a potential for more types due to the crystallographic complexity of the mineral. The strong fluorescence peaks varied between 1086 cm-1 and 1200 cm-1 depending on the type of Raman spectrum and are correlated with different types of REEs. Burbankite’s complex Raman signals require more investigation. We found it challenging to register the malachite’s external and internal modes. Due to the minerals’ eroded surfaces, we found a strong fingerprint of the host rock in two cases of three. Only the third malachite sample gave us results comparable with the RRUFF database. The -1 -1 strongest peak, V1 Ag, varied from 1086 cm to 1160 cm . This variety depends also on the -1 host rock’s effect. V1 at 1086 cm are most probably signals of the calcite matrix, while the peaks around 1160 cm-1 most probably belong to malachite. Our results from the experiment with ancylite differ from the RRUFF database. We believe that the additional doublet in the area of the internal modes of ancylite reveals the presence of impurities, most probably the presence of other rare earth metals. To prove or discard this hypothesis, a detailed chemical analysis needs to be performed. However, we think, that the deviations of the external modes most probably indicate signals being superimposed from the host rock, which, according to the peak positions, is likely to be calcite.

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6 Chapter II – Applications of Raman spectroscopy to gemmology

6.1 Background The portable Raman spectroscopy is a handy and easy-to-use technique in the modern gemmology. It is fast, sensitive, has micrometric spatial resolution and is non-destructive. It is used to collect information about the nature of gems, their chemical composition, structure and purity. Raman spectroscopy can aid in identifying inclusions, and thus in some cases even the gems’ provenance. It can also detect treatments done to the gems, such as enhancement and colouring (Bersani & Lottici, 2010). However, there are some limitations to Raman spectroscopy. Due to physical characteristics, some minerals respond very weakly to laser excitation, producing poor-quality signals which are difficult to interpret, such as black oxide inclusions, opal or cubic zirconia. Another challenge is noise – artefacts and non-Raman signals. They can arise from the instrument or from the environment, e.g. ambient light from electric lamps, sun or computer monitors (Dubessy et al., 2012).

6.1.1 Precious gemstones

6.1.1.1 Diamond, C Diamond is a metastable allotrope of carbon with the general formula C. It is less stable than graphite, but the conversion rate from diamond to graphite is very small at surface conditions. The crystal system is isometric-hexoctahedral (cubic) with symbol (4/m 3 2/m) and space group F d3m. Carbon atoms are arranged in a characteristic structure called diamond lattice, which is a variation of the face-centered cubic crystal structure. Diamond has a hardness of 10 on the Mohs scale, making it the hardest natural mineral (Wenk & Bulakh, 2012). Most diamonds are formed under the conditions of high temperature (>2000°C) and high pressure (35 GPa) which correspond to a depth of about 750 km. They are brought up to the surface by expanding volatile gas, which transports them through kimberlites, or pipes inside ultramafic rocks. Such pipes are formed usually in ultramafic rocks in very old continental shields, e.g. Yakutia (Siberia, Russia) or North-western Canada (Wenk & Bulakh, 2012). Raman spectroscopy is often used as a tool to diagnose and evaluate diamonds. It is the only compelling technique in the identification of black inclusions in natural diamonds. These

103 black inclusions are usually tiny pieces of graphite and are depicted on the Raman spectrum as a large peak at 1355 cm-1 (Dubessy et al., 2012). These inclusions can give very valuable information. Kagi et al. (2008) reported in one of their recent works that residual pressure around mineral inclusions in diamond can provide information about the depth of the diamond origin. This group developed three-dimensional Raman mapping system which allows for identification of differential stress between an inclusion and host diamond. The differential stress helps to calculate the depth of the diamond formation. The Raman spectrum of diamond is represented by the first-order Raman line at 1332 cm-1. Along with the high intensity of this peak, literature also suggests narrow full-width half- maximum (FWHM), which should be around 1.2 cm-1 (Prawer & Nemanich, 2004). The RRUFF database contains comprehensive information on diamonds’ Raman scattering (Figure 91).

Figure 91. Normalised RRUFF data on Raman scattering of diamond: R050204 (Source: Eric Van Valkenburg, Locality: Unknown); R050205 (Source: Eric Van Valkenburg, Locality: Unknown); R050206 (Source: Eric Van Valkenburg, Locality: Unknown); R050207 (Source: Eric Van Valkenburg, Locality: Unknown); X050052 (Source: Caltech, Locality: Plumas County, California, USA); X050053 (Source: G.R. Rossman 1989, Locality: Synthetic, General Electric); X050054 (Source: G.R. Rossman 1989, Locality: Synthetic, General Electric); X070001 (Source: Eric Van Valkenburg, Locality: Synthetic, DeBeers Element6); X080011 (Source: Gemological Institute of America 28754, Locality: Synthetic); R150105 (Source: Rock Currier, Locality: Synthetic by GE.); R150106 (Source: Rock Currier, Locality: Premier mine, Cullinan, Pretoria, Gauteng Province, South Africa); R150108 (Source: Rock Currier, Locality: Bushimaie River, Belgian Congo); R150107 (Source: Rock Currier, Locality: Zaïre); R150086 (Source: Michael Scott, Locality: unknown); R150087 (Source: Michael Scott, Locality: unknown); R150088 (Source: Michael Scott, Locality: unknown); R150089 (Source: Michael Scott, Locality: unknown).

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6.1.1.2 Red corundum, ruby, Al2O3 + Cr The precious gem-quality ruby is a variety of the mineral corundum, or aluminium oxide. Corundum has many varieties which are defined by the presence and nature of trace elements, such as chromium, iron, titanium and vanadium. The amount of trace elements can vary significantly depending on the geological conditions under which the gem was formed. For example, rubies from Greenland contain high amount of iron and low amount of vanadium, while rubies from Burma contain four times more iron than rubies from Thailand (Wenk & Bulakh, 2012; Sinha & Mishra, 2015). The crystal system of ruby is trigonal-hexagonal scalenohedral, with Hermann-Maugin group 3 2/m (Mineralogy Database, 1997). In the euhedral crystals of ruby, the oxygen atoms make up a hexagonal close packing, with trivalent aluminum and chromium occupying two thirds of the octahedral interstices, creating strong ionic-covalent bonds. These bonds are responsible for the high hardness of the mineral (9 on Mohs scale) and high density (4.0 g/cm3) (Wenk & Bulakh, 2012; Moss & Newnham, 1964). The infiltration of Cr3+ in the corundum lattice occurs due to a substitution reaction, when an Al3+ ion is replaced by a Cr3+ion. When Cr3+ is incorporated into the system, it does not occupy the same position as Al3+ did. Studies showed that Cr3+ occupies a site 0.06 Å from the normal Al3+ position, leaning towards the nearest Al neighbour, increasing the Cr-oxygen distance (Moss & Newnham, 1964). This fact makes the Raman spectrum of ruby distinct from the spectrum of other corundum types. Ruby has seven Raman active modes: 2A1g + 5 Eg = 7. The typical corundum vibrations are at 378, 418, 432, 451, 578, 645 and 751 cm-1 (Sinha & Mishra, 2015). However, not all vibrations are visible due to high fluorescence, produced by trace elements, the mechanism of which are still not completely understood (Ruby – Sapphire, 2010) (Figure 92). Xu et.al. (1995) reported that if Raman spectroscopic measurements are performed along the c-axis, some vibrations disappear, for example 578, 645 and 751 cm-1. However, they reappear again when the laser shines along the a-axis. While the amount of trace elements can tell about the geographical origin of the ruby, the full-width at half maximum (FWHM) can tell which ruby has a higher concentration of Cr3+. Gao et al. (2015) discusses that theoretically, a higher concentration of Cr3+ could mean bigger number of 3d electrons, which are in the same type of orbit but belong to different Cr3+ atoms in the ruby crystal. Since there is always a slight difference in their energy levels due to subtle differences in the electromagnetic environments, summarizing these differences together will widen the energy band. Consequently, the FWHM, which depends on the

105 excitation of 3d electrons, would also widen. However, this method requires further studying and evaluation of potential errors. The additional peaks are also not a rare phenomenon. One reason for their presence is structural disorder caused by dissolution of impurities, such as zircon, rutile or calcite inclusions that are known to exist in natural corundum. However, sometimes, additional peaks indicate trace of treatment. Sastry et al. (2009) distinguished an area between 200 and 400 cm- 1, which does not show any vibrations if the ruby is natural and untreated. However, it contains a few broad peaks if any type of heat or radiation treatment has been applied to the gem.

Figure 92. Normalised RRUFF data on Raman scattering of red corundum, ruby: R110096 (synthetic, Source: Gemmological Institute of America 10-12-2010-1), R110097 (synthetic, Source: Gemmological Institute of America 10-12-2010-2), R110116 (synthetic, Gemmological Institute of America 10-12-2010-21), X080009 (synthetic, Gemmological Institute of America 30078). Table 65. Chemical composition of the RRUFF red corundum samples. ID Chemical composition Comments R110096 Unknown Synthetic R110097 Unknown Synthetic R110116 Unknown Synthetic X080009 Unknown Synthetic

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6.1.2 Semi-precious gemstones

6.1.2.1 Peridot, Mg2SiO4 Peridot is a gem-quality forsterite, Mg-rich olivine. There are two end-members in olivine’s

solid solution: forsterite (Mg2SiO4) and fayalite (Fe2SiO4). Olivine has orthorhombic

symmetry, where each oxygen from the isolated SiO4 tetrahedra is shared by three octahedral cations. The oxygen atoms build close-packing layers, where the gaps between layers are filled with magnesium and iron. The octahedral cations are arranged in a chain perpendicular to the a-axis (Wenk & Bulakh, 2012). This is the ideal representation of olivine’s symmetry, however, in reality, there are distortions in the lattice. There are two types of octahedral metals: M1 and M2. They differ in shape and symmetry: M1 is located at centre of symmetry (I), while M2 is located on mirror planes (m). M1 diverges more significantly from the ideal octahedral geometry than M2, while M2 has a shorter average M–O bond length. The degree

of SiO4 distortion due to M1 and M2 deviations is higher in forsterite than in fayalite. The reason for this is the ionic radius of Fe2+ (in fyalite) which is larger than than Mg2+ (forsterite), meaning that the M1 and M2 octahedral of fayalite are more like each other than those of forsterite (Kuebler et al., 2006). Olivine has 84 normal vibrational modes. There are 81 modes which are optically active

and 36 modes that are Raman active: 11 Ag, 11 B1g, 7 B2g, 7 B3g (Bonilla, 1982). Bonilla (1982) distinguished such Raman shifts in his work, studying Raman spectra of fosterite.

Table 66. Raman shifts of fosterite (Bonilla, 1982). -1 -1 -1 -1 Ag (cm ) B1g (cm ) B2g (cm ) B3g (cm ) Internal: 970, 864, 834, 610, Internal: 922, 588, 405, 368, 964, 858, 828, 610, 580, 430, 418, 316, 832, 584, 439, 309, 250, 210 545, 420 212, 180, 150 External: External: 355, 305, 239, 160 335, 330, 302, 224, 154

In summary, the Raman spectrum of olivine can be divided into three main regions: < 400 cm- 1, 400-700 cm-1 and 700-1100 cm-1. Peaks below 400 cm-1 are the result of rotational and 2+ translational motions of SiO4 as a unit, and translational motions of octahedral cations (Mg and Fe2+) in the crystal lattice of the mineral. Peaks in the 400–700 cm-1 spectral interval are

assigned to internal bending vibrational modes of the SiO4 tetrahedron. The spectral region of

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700-1100 cm-1 is the most interesting part, because there can be found the specific-for-olivine doublet (Table 65, Figure 92). Peaks from this region depict the internal stretching vibrational modes of the SiO4 ionic tetrahedron. The peak positions of the doublet vary depending on the chemical composition of the mineral across the continuum of Mg/(Mg + Fe). Kuebler et al. (2006) presented the analytical system in one of their latest works which allows for identification of the chemical (Fo–Fa) compositions of olivine from Raman spectral peak positions. According to this system, the first peak from the doublet (DB1) has an approximate range of 10 wavenumbers: from 815.0 cm-1 in the fayalite spectrum to 824.8 cm-1 in the forsterite spectrum. The second peak from the doublet pair (DB2) is the most characteristic, helping to distinguish between forsterite and fayalite. The second peak has a range of approximately 20 wavenumbers: from 837.8 cm-1 in fayalite to 856.7 cm-1 in forsterite. Besides the wavenumbers’ range, another important distinctive feature of the DB2 is the shape: Fe-rich olivine (Fo<50) has less distortion in the lattice (due to greater similarity of the octahedral M1 and M2) than Mg-rich olivine and, thus, the DB2 peak often appears as a shoulder on the DB1 peak, not as a well-developed separate peak. However, some authors claim that the octahedral M1 does not contribute to Raman scattering. McKeown et al. (2010) reported in his recent work that the Mg1 atoms occupy centrosymmetric sites and, thus, cannot contribute to Raman shift in forsterite’s spectra. As it was mentioned above, M2 is in the mirror plane in relation to M1, which means that the inversion symmetry gives increasing deviations and thus, M2 is mainly responsible for the Raman scattering. The RRUFF database contains comprehensive information on forsterite’s Raman scattering (Figure 93, Table 66).

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Figure 93. Normalised RRUFF data on Raman scattering of forsterite: R040018 (Source: Bob Downs, Locality: Trudy's mine, San Carlos, Gila County, Arizona, USA), R040052 (Source: Hideki Kanazawa of Kyoto University, Japan, Locality: Synthetic, Czochralski method), R040057 (Source: Bob Downs, Locality: Trudy's mine, San Carlos, Gila County, Arizona, USA), R050117 (Source: Farooq and Nazia Sawal, Locality: Sapat, Gilgit, Pakistan), X050080 (Source: G.R. Rossman 1017, Locality: synthetic end member), X050081 (Source: G.R. Rossman 1000, Locality: East Africa), X050082 (Source: G.R. Rossman 1001, Locality: Morales), X050085 (Source: G.R. Rossman 889, Locality: Zabargad), X050086 (Source: G.R. Rossman 1345, Locality: Sri Lanka), X050087 (Source: G.R. Rossman 1107, Locality: China), X050089 (Source: RD Shannon 62047- 46, Locality: Unknown), X050090 (Source: Caltech, Locality: San Carlos, Arizona, USA), R060539 (Source: Gemological Institute of America 19488, Locality: Sri Lanka), R060535 (Source: Gemological Institute of America 3600, Locality: Unknown), R060551 (Source: Gemological Institute of America 25, Locality: Kohiston, Pakistan), R100099 (Source: American Museum of Natural History 110942, Locality: Synthetic), R100100 (Source: American Museum of Natural History 75382, Locality: Scott Creek, Jackson County, North Carolina, USA), R100101 (Source: American Museum of Natural History 75156, Locality: Yancey County, North Carolina, USA), R100140 (Source: William W. Pinch, Locality: Pakistan). Table 67. Chemical composition of the RRUFF forsterite samples. Sample ID Chemical composition Comments R040018 (Mg1.81Fe0.18Ni0.01) Σ=2Si1.00 The most

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O4; trace amounts of Mn and Ca “contaminated” chemistry R040052 Mg2.00 Si1.00 O4 Sample with the most ideal chemistry R040057 (Mg1.67Fe0.32Ni0.01) Σ=2Si1.00 The most

O4; trace amounts of Mn and Ca contaminated chemistry R050117 (Mg1.81Fe0.18Ni0.01) Σ=2Si1.00

O4 X050080 Unknown

X050081 Unknown

X050082 Unknown

X050085 Unknown

X050086 Unknown

X050087 Unknown

X050089 Unknown

X050090 Unknown

R060539 (Mg1.67Fe0.33) Σ=2Si1.00 O4; trace amounts of Mn and Ca R060535 (Mg1.81Fe0.18Ni0.01) Σ=2Si1.00

R060551 (Mg1.82Fe0.18) Σ=2Si1.00 O4; trace amounts of Mn R100099 (Mg1.998Ca0.002Zn0.001)

Σ=2.001 Si1.000 O4 R100100 (Mg1.832 Fe0.153 Ni0.008 Mn0.00 The most

2Zn0.001) Σ=1.996 Si1.000 O4 “contaminated” chemistry

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R100101 (Mg1.809Fe0.183Ni0.008Mn0.003)

Σ=2.003 Si0.999 O4 R100140 Unknown

Among the RRUFF samples of forsterite, sample with ID R040052 has the most ideal chemistry. Three samples have the most “contaminated” chemical composition: R040018, R040057, and R100100.

6.1.2.2 Azurite, Cu3(CO3)2(OH)2 Azurite is one of the two copper carbonate minerals. The first one is malachite, and azurite is therefore often accompanied by it. Azurite is a component of a copper ore. However, it has been mostly used in production of blue paint and as a gemstone. Malachite is also used as a gemstone, but azurite is rarer than malachite and is therefore considered to be more valuable. On the Mohs scale azurite has a hardness of only 3.5 to 4 – it is a fairly soft stone, that is why it is not used in jewellery very often.

The crystal symmetry of azurite is monoclinic-prismatic (2/m) with space group P 21/a, where the copper cations are linked to carbon and oxygen anions (Wenk & Bulakh, 2012). The Raman scattering properties of azurite are not as well studied as for diamond or peridot. However, because azurite has been used as a paint, there are a few authors who studied azurite as historical artefact, exhaustively covering the subject. The typical Raman spectrum of azurite contains modes of three separate vibrational groups: OH, CO3 and Cu–O. Raman scattering of azurite is based upon a distorted square planar arrangement in the monoclinic structure. The mineral’s structure incorporates two types of Cu cations, both in distorted square planar system in relation to two hydroxyl groups and two CO3 atoms (Frost et al., 2002). The Raman spectrum of azurite creates a complicated picture. Frost et al. (2002) named

Raman active modes of carbonate ions and Cu-O: 6Ag, 6Bg, 6Au, 6Bu and skeletal vibrations:

2Ag, 1Bg, 2Bu, 2B2u, 2B3u. The situation with the OH vibration modes is more complicated since it is difficult to register them (Table 67).

Table 68. A comparative table of Raman bands of azurite, based on works of Buzgar & Apopei (2009), Mattei et al. (2008) and Frost et al. (2002). Assignment Buzgar & Apopei Mattei et al. (2008) Frost et al. (2002) (2009)

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T(Cu, CO3) 250, 285, 339, 404, 157, 174, 182, 240, 112, 131, 139, 144, 544 250, 267, 282, 332, 154, 165, 171, 179, 387, 402, 542 194, 215, 237, 248, 265, 281, 332, 387, 400, 414, 540

ν4-Symmetric CO3 766 744, 768 739, 764 bending mode

ν2-Asymmetric CO3 835 840 815, 835 bending mode O-H out-of-plane 939 937 952 bending mode

ν1-Symmetric CO3 1097 1099 1095 stretching mode

ν3-Asymmetric CO3 1425, 1459 1422, 1433, 1462 1421, 1431 stretching mode O-H bending mode 1579 1582 Not observed O-H stretching mode Not observed 3431 3424, 3446

The RRUFF database contains poor amount of information on azurite’s Raman scattering, only two Raman bands (Figure 94, Table 68). Both RRUFF samples have ideal chemistry and do not contain impurities.

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Figure 94. Normalised RRUFF data on Raman scattering of azurite: R050497 (Source: Marcus Origlieri, Locality: Tsumeb mine, Tsumeb, Otavi District, Oshikoto, Namibia), R050638 (Source: University of Arizona Mineral Museum 13399, Locality: Zacatecas, Mexico).

Table 69. Chemical composition of the RRUFF azurite samples. ID Chemical composition Comments R050497 Cu3.00(CO3)2(OH)2 No impurities R050638 Cu3.00(CO3)2(OH)2 No impurities

Azurite has a characteristic intense peak at 400 cm-1, according to Frost et al., 2002, or at 404 cm-1, according to Buzgar & Apopei ,2009. The peaks < 600 cm-1 are responsible for the -1 translation mode of Cu and CO3. The peaks < 1600 cm depict modes of CO3 complex, including ν1-Symmetric, ν2 -Asymmetric, ν4-Symmetric bending modes and ν3-Asymmetric CO3 stretching mode. Azurite can contain impurities. Aru et al. (2014) reported in his recent work that they managed to identify inclusions of malachite, hematite, goethite, cuprite, rutile and anatase in azurite samples with the help of Raman spectroscopy.

6.1.2.3 Fluorite, CaF2

Fluorite is a gem quality mineral with the formula CaF2. It belongs to the group of Halides. The F- anion is a chemically very active and, thus, ionizes easily with metallic cations by incorporating an electron in its lattice. The most common halogen elements are of alkali character, such as sodium, potassium, calcium, magnesium and strontium. Therefore, the

113 easily attracted anion F- builds strong chemical bonds with calcium, creating the widespread mineral fluorite (Wenk & Bulakh, 2012). The most common crystal form of fluorite is primitive cube; however, it can sometimes build octahedra. It has the isometric-hexoctahedral crystal system (4/m 3 2/m) and space group F m3m (Mineralogy Database, 1997). Fluorite can be confused with calcite or quartz. However, it is possible to distinguish them due to difference in hardness. Calcite is softer (Mohs scale 3) than fluorite (Mohs scale 4), while quartz is much harder (Mohs scale 7). However, in the case of intergrowth of fluorite and calcite, to separate those relying only on observations can be very difficult. Fluorite has a wide range of colours: white, purple, blue, red, pink, orange, yellow, brown, green, grey, and black. It can also be colourless or banded. A pure fluorite, free from impurities, is colourless. Thus, the fluorite’s colour depends on the nature of impurity and inclusions incorporated in the crystal structure. Sometimes organic substances can cause fluorite’s colouring, such as hydrocarbons. It is common that the colouring elements belong to the rare earth elements group (REE) (Wenk & Bulakh, 2012). However, there is a lack of scientific reports explaining exactly which metals or REE could be responsible for which colours. Such studies would be crucial for Raman spectroscopy analysis of different varieties of fluorite. Due to the simple crystal structure, fluorite has only one Raman active photon (Keramidas

& White, 1973): 1T2g = 1. This Raman active mode shows both Stokes and anti-Stokes at Raman shift of 322 cm-1 (Russell, 1965; Gee et al., 1965; Keramidas &White, 1973; Burruss et al., 1992). However, already in the 60s and the 70s scientists started to discuss the problem of additional signals. Pure fluorite is supposed to give just one Raman active signal at room temperature (around 300°K). But pure minerals are very rare in nature. Even a fully transparent, colourless fluorite can contain other chemical elements than calcium and fluorine. Thus, Russell (1965) and Gee et al. (1965) discovered 14-18 additional Stokes and linked it with the presence of REE. This subject received a lot of attention in the scientific community and was studied extensively by solid-state physicists (for example, Hayes (1974), Tarashchan (1978), Wright (1990)). But this problem was studied mostly only in synthetic fluorite and with focus on the fluorescence spectra of individual REE. The first article summarising all known REE luminescence spectra in fluorite of natural abundance was published in 1992. Burruss et al. (1992) presented general characteristics of the fluorescence spectra which they divided into 9 areas, where each band’s area (in nm) was linked to certain REEs. 114

Additional bands caused by the presence of REE have received such attention, that the studies on the main fluorite’s Raman Stoke and anti-Stoke at 322 cm-1 are scarce in literature. Its presence and character are taken for granted. Except for the possible shift of the peak, which could be caused by impurities, the main peak can have different intensities. The RRUFF database contains five studied samples of fluorite: one blue, two purple fluorites, one colourless and one pale green fluorite. The blue fluorite (ID: R060548) has a weak peak at 322 cm-1 with a relatively small intensity (Figure 95). Both purple fluorites (ID: R040099 and ID: R050046) have well-developed peaks with strong intensity (Figure 96). Literature suggests that colourless, transparent fluorite without visible impurities should have a single peak at 322 cm-1 at 300° K (Russell, 1965; Gee et al., 1965; Keramidas &White, 1973). However, the only RRUFF colourless fluorite (ID: R050115), with no impurities, lacks this peak at 322 cm-1 (Figure 97). The pale green RRUFF sample (ID: R050045) has a strong peak at 322 cm-1, it is as developed as the purple fluorites’ bands (Figure 97). Besides, the pale green fluorite lacks any other peaks and matches best with the described colourless transparent fluorite in literature. In this study, the focus was on the main peak’s intensity. 8 fluorite samples were analysed: 3 blue, 2 purple, 2 white (one semi-transparent, another is opaque) and 1 grey. The aim was to compare the results with literature and RRUFF to discuss what possible reasons can influence the main peak intensity. Also, the aim was to apply the portable Raman to find out whether the method is suitable for REE identification.

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Figure 95. Raman spectroscopy of blue fluorite, ID: R060548 (Source: Gemological Institute of America 18, Locality: unknown).

Figure 96. Raman spectroscopy of two purple fluorites. ID: R040099 (Source: Bob Downs, Locality: Rock Candy mine, Grand Forks, British Columbia, Canada) and ID: R050046 (Source: Eugene Schlepp, Locality: Shangbao, Lei Yang, Hunan Province, China).

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Figure 97. Raman spectra of colourless fluorite, ID: R050115 (Source: Syed Shah, Locality: Isthak Valley Iskardu, N.A. Gilgit, Pakistan) and pale green fluorite, ID: R050045 (Source: Eugene Schlepp, Locality: Hunan Province, China). Table 70. Chemical composition of the RRUFF azurite samples. ID Colour Chemical composition Comments

R060548 blue Ca1.00F2.00 No impurities

R040099 purple Ca0.99F2.00 No impurities

R050046 purple Ca1.000 F2.000 No impurities

R050115 colourless Ca1.000 F2.000 No impurities

R050045 Pale green Ca1.000 F2.000 No impurities

As it is visible in Table 70, the microprobe did not identify the presence of impurities or REE in the RRUFF samples. All five samples have an ideal chemistry, except R040099, which has

Ca0.99, this may imply undetected impurities. Their Raman spectrum varies and doesn’t match with each other. Is it instrumental failure or does this phenomenon have geochemical explanation? To answer these questions, the above 8 described samples were studied.

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6.2 Results

6.2.1 Precious gemstone

6.2.1.1 Diamond

Figure 98. Diamond specimen. Description: a quarter of a diamond, crashed by pressure, fully transparent, no visible inclusions. Source: Research collection at the department of Earth Sciences, Uppsala University. Raman spectroscopy showed one characteristic peak for diamond (Table 70, Figure 99).

Table 71. Raman peaks and FWHM of the diamond sample. N of Raman spectrum Wavenumber (cm-1) FWHM

1 1332.1 ± 0.02 6.5

2 1332.1 ± 0.04 7.8

3 1332.1 ± 0.03 7.7

4 1332.0 ± 0.02 6.4

5 1332.0 ± 0.02 6.4

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Figure 99. Normalised Raman bands of the diamond sample.

6.2.1.2 Red corundum, ruby

6.2.1.2.1 Red corundum 1

Figure 100. Red corundum, sample 1.

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Description: 2-6 mm spherical crystals in dark grey matrix. Source: Mineral collection at the department of Earth Sciences, shelf N 26, Uppsala University. Raman spectroscopy showed following results (Table 71, Figure 101):

Table 72. Raman peaks and FWHM of red corundum, sample 1. Raman shift (cm-1) FWHM Comments 257.2 – 259.5 55.3 – 65.7 Additional peak caused by natural heating (regional metamorphism)/irradiation source

415.2 – 415.3 9.2 – 12.1 A1g, shifted

441.4 – 442.4 41.2 – 43.4 Eg, shifted 610.2 39.4 – 44.0 Impurity/fluorescence 1266.1 – 1274.0 38.6 – 93.8 Impurity/fluorescence 1350.6 – 1365.5 44.7 – 51.9 Impurity/fluorescence 1451.7 – 1470.4 50.9 – 66.8 Impurity/fluorescence 1601.3 – 1609.6 70.6 – 75.4 Impurity/fluorescence 1622.2 - 1623.2 97.2 – 142.7 Impurity/fluorescence

Crystal Sleuth RRUFF search engine identified 51% match with rutile, 51 % with corundum, 50% with zircon and 46% with quartz.

Figure 101. Normalised Raman bands of the red corundum, ruby, sample 1.

6.2.1.2.2 Red corundum 2

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Figure 102. Red corundum, sample 2. Description: spherical, 2 mm, pinkish-red, Source: USA. Source: Research collection at the department of Earth Sciences, Uppsala University.

Table 73. Raman peaks and FWHM of red corundum, sample 2. Raman shift (cm-1) FWHM Comments

415.1 – 415.3 9.6 – 10.7 A1g

642.9 – 643.3 11.1 – 13.2 Eg, very weak

1086.1 – 1086.2 10.0 – 10.7 Eg

Figure 103. Normalised Raman bands of the red corundum, ruby, sample 2.

6.2.1.2.3 Red corundum 3

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Figure 104. Red corundum, sample 3. Description: spherical, 2 mm, pinkish-red, Source: Switzerland. Source: Research collection at the department of Earth Sciences, Uppsala University.

Table 74. Raman peaks and FWHM of red corundum, sample 3. Raman shift (cm-1) FWHM Comments

414.8 – 415.1 9.9 – 11.8 A1g

642.4 – 642.8 12.6 – 14.5 Eg

1085.9 – 1086.4 9.2 – 12.1 Eg

Figure 105. Normalised Raman bands of the red corundum, ruby, sample 3.

6.2.2 Semi-precious gemstones

6.2.2.1 Peridot

6.2.2.1.1 Peridot, sample 1.

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Figure 106. Peridot, sample 1. Description: small fragment (2-3 cm long), green coloured, spherical shape, semi-transparent. Source: Research collection at the department of Earth Sciences, Uppsala University.

Table 75. Raman spectroscopy results of peridot, sample 1. -1 -1 -1 -1 Ag (cm ) B1g (cm ) B2g (cm ) B3g (cm ) Additional Internal: 961.8 – 963.7 absent 272.0; 917.8 – 471.7 822.7 (DB1), 918.3 854.9 – 855.1 (DB2); 961.8 – 963.7

Full width at half maximum (FWHM) of the doublet varies between 10.2 and 11.4 for the -1 DB1 and between 12.3 and 13.0 for the DB2. FWHM for B3g (917.8 – 918.3 cm ) varies -1 between 6.9 and 9.9. FWHM for B1g (961.8 – 963.7cm ) has the widest range, from 5.0 to 36.5. Raman spectroscopy of the first peridot (forsterite) sample clearly showed a well- developed doublet, 1 Ag, 1 B1g, 2 B3g and one additional Raman active peak. B2g peaks are absent (Figure 107).

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Figure 107. Normalised Raman bands of the first forsterite sample.

6.2.2.1.2 Peridot, sample 2

Figure 108. Peridot, sample 2. Description: three small fragments (1-2 cm long), green coloured, round shape, semi- transparent. Source: Research collection at the department of Earth Sciences, Uppsala University.

Table 76. Raman spectroscopy showed following results. -1 -1 -1 -1 Ag (cm ) B1g (cm ) B2g (cm ) B3g (cm ) Additional Internal: 426.5 – 428.7; Absent 366.7; 917.7 – 296. 4- 296.9; 603.3 – 604.3; 583. 3 – 584.9; 918.4 822.1 – 822.4 (DB1); 854.6 – 854.8 (DB2); 960.7 – 961.3

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External: 218.0 – 221.1;

Full width at half maximum (FWHM) of the doublet varies from 11.7 to 11.9 for DB1 and -1 from 12.8 to 13.3 for DB2. FWHM for internal Ag (603.3 – 604.3 cm ) varies between 14.0 -1 and 17.5, another internal Ag (960.7 – 961.3 cm ) varies from 17.9 to 21.8. External Ag has FWHM between 19.6 and 60.1. -1 FWHM for B1g (426.5 – 428.7 cm ) varies from 17.2 to 49.6. Another B1g (583.3 – 584.9 -1 -1 cm ) has FWHM between 19.2 to 20.7. FWHM for B3g (366.7 cm ) is 18.3. Another B3g (917.7- 918.4 cm-1) has FWHM between 8.9 and 9.5. The additional peak lies at 296.4 – 296.8 cm-1 and has FWHM between 12.5 and 17.3. Raman spectroscopy of the second peridot (forsterite) sample showed a well-developed doublet, 2 Ag internal, 1 Ag external, 2 B1g, 2 B3g and one additional Raman active peak. B2g peaks are absent (Figure 109).

Figure 109. Normalised Raman bands of the second forsterite sample.

6.2.2.1.3 Olivine, sample 3

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Figure 110. Olivine, sample 3. Description: fragment 5-6 cm long, green coloured, semi-transparent. Source: Research collection at the department of Earth Sciences, Uppsala University.

Table 77. Raman spectroscopy results of olivine, sample 3. -1 -1 -1 -1 Ag (cm ) B1g (cm ) B2g (cm ) B3g (cm ) Additional Internal: 431.8 – 435.2; Absent 918.1 – 918.9 298. 7 – 300.9 542. 4; 823.3 – 583.4 – 606.6; 823.8 (DB1); 855.8 – 856.4 (DB2); 962. 6 – 965.0 External: 214. 3 – 222. 7

Full width at half maximum (FWHM) of the doublet varies from 10.3 to 11.1 for DB1 and -1 from 10.9 to 14.4 for DB2. Internal Ag (542.4 cm ) has FWHM at 18.1. Another internal Ag -1 -1 (962.6 – 965.0 cm ) has FWHM between 15.2 and 20.8. External Ag (214.3 – 222.7 cm ) has FWHM between 5.9 and 7.8. -1 FWHM for B1g first peak at 431.8 – 435.2 cm is between 17.2 and 19.8, for the second -1 peak at 583.4 – 606.6 cm varies significant between 14.4 and 58.4. FWHM for B3g (918.1 - -1 -1 918.9 cm ) is between 7.9 to 9.7. B2g is absent and one additional peak at 298.7 – 300.9 cm has FWHM between 15.1 and 20.6.

Raman spectroscopy of the third sample, olivine, showed a well-developed doublet, 2 Ag internal, 1 Ag external, 2 B1g, 1 B3g and one additional Raman active peak. B2g peaks are absent (Figure 111).

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Figure 111. Normalised Raman bands of the third sample, olivine. Comparative analysis between the most “contaminated” RRUFF sample (ID: R100100), RRUFF sample with the most ideal chemistry (ID: R040052) and the first forserite (peridot) sample:

Figure 112. Comparison between RRUFF most ”contaminated” sample (R100100), sample with the most ideal chemistry (R040052) and the first forsterite (peridot) sample.

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Comparative analysis between the most “contaminated” RRUFF sample (ID: R100100), RRUFF sample with the most ideal chemistry (ID: R040052) and the second forserite (peridot) sample:

Figure 113. Comparison between RRUFF most” contaminated” sample (R100100), sample with the most ideal chemistry (R040052) and the first forsterite (peridot) sample. Comparative analysis between the most “contaminated” RRUFF sample (ID: R100100), RRUFF sample with the most ideal chemistry (ID: R040052) and the third sample, olivine:

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Figure 114. Comparison between RRUFF most” contaminated” sample (R100100), sample with the most ideal chemistry (R040052) and the third sample, olivine.

6.2.2.1.4 Azurite

6.2.2.1.4.1 Azurite, sample 1

Figure 115. Azurite, sample 1. Description: crystalline aggregate of dark-blue colour, every crystal is approximately 1-3 cm long. Source: Mineral collection of the Naturhistoriska riksmuseet in Stockholm.

Table 78. Raman spectroscopy results of azurite, sample 1. Assignment Raman shift (cm-1) FWHM Comments T(Cu, CO3) 134.7 4.7 – 6.4

129

150.9 5.3 197.0 - 198.4 4.6 - 4.7 261.0 5.1 395.8 – 399.5 4.5 – 16.9 413.0 6.9 Slightly shifted main intense peak

ν4-Symmetric CO3 Not observed Not observed bending mode

ν2-Asymmetric CO3 816.9 4.0 bending mode O-H out-of-plane Not observed Not observed bending mode

ν1-Symmetric CO3 1095.5 – 1096.3 8.6 – 16.2 stretching mode

ν3-Asymmetric CO3 Not observed Not observed stretching mode O-H bending mode Not observed Not observed

O-H stretching mode Not observed Not observed

Additional 445.2 4.3 560.8 3.8 1075.1 3.8 1226.0 3.4 1300.3 3.3 1347.3 5.3 1845.5 5.3 1914.6 3.6 1931.5 2.5 2041.5 2.9 2051.7 2.5 2065.9 2.9 2078.6 4.9 doublet 2083.8 2.8 doublet

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Figure 116. Normalised Raman bands of azurite, sample 1.

6.2.2.1.4.2 Azurite, sample 2

Figure 117. Azurite, sample 2. Description: small fragment of the spherical shape, light blue coloured. Source: Research collection at the department of Earth Sciences, Uppsala University.

Table 79. Raman spectroscopy results of azurite, sample 2. Assignment Raman shift (cm-1) FWHM Comments T(Cu, CO3) 192.7 – 196.4 25.1 – 36.1 394.6 14.4 460.5 – 461.4 14.0 – 14.9 Significantly shifted main peak

131

ν4-Symmetric CO3 Not observed Not observed bending mode

ν2-Asymmetric CO3 Not observed Not observed bending mode O-H out-of-plane Not observed Not observed bending mode

ν1-Symmetric CO3 Not observed Not observed stretching mode

ν3-Asymmetric CO3 1473.2 44.8 Poor-developed triple stretching mode peak O-H bending mode Not observed Not observed

O-H stretching mode Not observed Not observed

Additional 118.0 – 119.1 13.8 – 14.5 350.9 11.4 1244.4 – 1245.8 135.0 – 155.3 Doublet 1395.0 3.2 1592.0 3.2 2017.5 2.8

Figure 118. Normalised Raman bands of azurite, sample 2.

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6.2.3 Fluorite

Figure 119. Fluorite specimens. Among 16 samples presented at the Mineralogical Collection of the Department of Earth Sciences, shelf N 37, at Uppsala university, 4 specimens were chosen for the analysis. Additional 4 minerals were provided by the Department of Earth Sciences and were selected from the Research Collection.

6.2.3.1.1 Fluorite 1.

Figure 120. Fluorite, sample 1. Description: small fragment, 1 cm long, crystal structure is not clear, blue colour. Source: Research collection at the Department of Earth Sciences, Uppsala University.

Table 80. Raman spectroscopy results of fluorite, sample 1. Raman shift (cm-1) FWHM Comments 322 Absent Absent 1144.2 – 1150.6 20.7 – 59.6 Broad, has shoulder 1242.8 – 1245.5 40.7 – 49.2 Broad 1349.3 – 1350.5 30.0 – 34.3 Broad 1779.9 – 1780.0 8.1 – 10.0

133

1881.9 – 1882.5 16.0 – 17.0

Figure 121. Normalised Raman bands of fluorite 1, blue.

6.2.3.1.2 Fluorite 2.

134

Figure 122. Fluorite, samples 2, 3 and 4.

Description: 5 cm long crystal, octahedral, blue. Source: Research collection at the department of Earth Sciences, Uppsala University.

Table 81. Raman spectroscopy results of fluorite, sample 2. Raman shift (cm-1) FWHM Comments 322 Absent Absent 1141.4 – 1147.3 35.4 – 64.5 Broad 1243.2 – 1243.7 40.5 – 44.6 Broad 1350.5 – 1351.5 29.8 – 39.4 Broad 1777.7 – 1780.3 7.4 – 21.1

1882.4 – 1882.6 16.0 – 17.7

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Figure 123. Normalised Raman bands of fluorite 2, blue.

6.2.3.1.3 Fluorite 3. Description: 5 cm long crystal, octahedral, blue. Source: Research collection at the department of Earth Sciences, Uppsala University.

Table 82. Raman spectroscopy results of fluorite, sample 3. Raman shift (cm-1) FWHM Comments 181.8 – 182.0 38.6 – 41.3 Broad 322 Absent Absent 381.0 – 382.6 35.4 – 49.3 Broad 1142.4 – 1145.0 40.6 – 50.3 Broad 1243.7 – 1243.8 37.0 – 39.8 Broad 1351.2 – 1351.9 35.2 – 39.0 Broad 1776.7 – 1776.9 19.3 – 20.4 Broad 1876.6 – 1879.6 15.0 – 15.1

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Figure 124. Normalised Raman bands of fluorite 3, blue.

6.2.3.1.4 Fluorite 4. Description: 5 cm long crystal, octahedral, purple. Source: Research collection at the department of Earth Sciences, Uppsala University.

Table 83. Raman spectroscopy results of fluorite, sample 4. Raman shift (cm-1) FWHM Comments 214.1 – 214.2 6.5 – 9.4

318.4 13.8 – 14.3 Main peak, shifted towards lower numbers 982.6 – 983.5 32.4 – 36.2

1123.9 – 1124.4 15.9 – 20.8

1151.8 – 1152.6 11.5 – 18.0

1249.0 – 1249.5 34.4 – 37.1

1326.4 – 1327.7 67.3 – 81.2

1452.4 – 1453.6 62.7 – 75.8

137

1720.9 – 1722.0 21.0 – 28.8

1821.8 – 1822.5 16.8 – 24.7

1875.9 – 1879.6 14.6 – 15.2

1932.9 – 1933.2 7.6 – 8.0

1958.1 – 1958.3 7.9 – 8.7

Figure 125. Normalised Raman bands of fluorite 4, purple.

6.2.3.1.5 Fluorite 5.

Figure 126. Fluorite, sample 5. Description: purple fragments of mineral in quartz rich matrix, 10-15 cm long. Source: Mineral collection at the department of Earth Sciences, Uppsala University.

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Table 84. Raman spectroscopy results of fluorite, sample 5. Raman shift (cm-1) FWHM Comments 318.3 – 319.4 12.0 – 15.3 Main peak, shifted towards lower numbers 1149.2 – 1150.2 13.5 – 18.9

1190.3 – 1193.6 45.4 – 66.2 Broad 1235.5 – 1253.4 21.7 – 23.2

1320.2 – 1321.4 42.8 – 48.4 Broad 1456.1 – 1463.4 51.4 – 104.6 Broad 1684.7 – 1886.0 19.0 – 22.2

1721.2 – 1722.2 17.3 – 27.2

Figure 127. Normalised Raman bands of fluorite 5, purple.

6.2.3.1.6 Fluorite 6.

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Figure 128. Fluorite, sample 6. Description: white, opaque mineral fragments in dark grey matrix, which is 10-15 cm long. Source: Mineral collection at the department of Earth Sciences, Uppsala University.

Table 85. Raman spectroscopy results of fluorite, sample 6. Raman shift (cm-1) FWHM Comments 150.4 – 151.0 14.9 – 19.5

278.0 – 279.3 16.9 – 18.7

710.8 – 711.7 8.2 – 13.0

1086.1 – 1086.4 6.2 – 6.3

1205.9 – 1209.5 50.0 – 85.7 Broad 1302.4 – 1303.2 28.7 – 33.2 Broad 1390.8 – 1391.8 30.2 – 32.9 Broad 1435.5 – 1487.9 3.9 – 6.1

1551.0 37.1 - 59.1 Broad 1670.9 – 1672.6 52.6 – 60.9 Broad 1845.5 – 1846.0 29.1 – 35.6 Broad

140

Figure 129. Normalised Raman bands of fluorite 6, white, opaque. The experiment’s results do not match with neither literature nor RRUFF database on fluorite. Crystal Sleuth search engine did not give any reasonable match, for example, showing 73% match with graphite, which can be discarded due to observational conclusions. Thus, manual searching was performed for the reasonable candidate for this Raman spectroscopy (Figure 130). The mineral is white and opaque and has the external similarity with calcite. It is also soft, therefore, we conclude that this mineral is not fluorite, but calcite with fluorite “fingerprint”, which was placed among fluorites by mistake.

Figure 130. Comparison between fluorite sample 6 and calcite sample 2.

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6.2.3.1.7 Fluorite 7.

Figure 131. Fluorite, sample 7. Description: 5-6 cm long transparent, colourless crystals in aggregate. Source: Mineral collection at the department of Earth Sciences, Uppsala University.

Table 86. Raman spectroscopy results of fluorite, sample 7. Raman shift (cm-1) FWHM Comments 152.0 – 152.0 13.4 – 14.7

279.0 – 279.3 16.2 – 16.9

712.0 – 712.4 7.6 – 7.9

1086.5 – 1086.7 5.9 – 6.1

1293.8 – 1299.7 42.8 – 110.7

1390.3 – 1391.9 25.6 – 41.3

1846.4 – 1847.0 25.9 – 36.5

Only the area between 0 and 1080 cm-1 was tested by Crystal Sleuth. This area showed to have 77% match with calcite (Figure 132).

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Figure 132. Results from Crystal Sleuth RRUFF searching engine from the area between 0 to 1080 cm-1 of fluorite 7. Manual matching of the experiment’s Raman spectrum with RRUFF colourless fluorite and RRUFF colourless calcite anti-Stokes:

Figure 133. Comparison between experiment’s colourless fluorite with RRUFF colourless fluorite and RRUFF colourless calcite Raman spectrum.

6.2.3.1.8 Fluorite 8. 143

Figure 134. Fluorite, sample 8. Description: single crystal in white sedimentary matrix. Source: Mineral collection at the department of Earth Sciences, Uppsala University.

Table 87. Raman spectroscopy results of fluorite, sample 8. Raman shift (cm-1) FWHM Comments 113.2 – 116.6 18.3 – 33.2

240.6 – 241.1 32.2 – 34.0 Broad 318.2 – 318.4 12.2 – 14.1 Main peak 1162.2 – 1163.2 37.2 – 55.7 Broad 1245.9 – 1247.5 36.7 – 50.7 Broad 1346.8 – 1348.8 25.2 – 37.6 Broad 1536.7 – 1538.6 42.6 – 70.7 Broad 1630.2 – 1637.5 29.6 – 38.2 Broad 1879.7 – 1879.9 15.4 – 16.4

144

Figure 135. Normalised Raman bands of fluorite 8, grey, semi-transparent.

6.3 Discussion

6.3.1 Precious gemstone

6.3.1.1 Diamond Raman spectroscopy showed only one peak for all Raman spectra taken from the sample. The peak is located at 1332 cm-1 which is very characteristic for a diamond (Prawer & Nemanich, 2004). Raman spectroscopy did not identify neither shifts nor additional peaks of impurities. The only difference, which was observed was the intensity parameters and the full-width at half maximum (FWHM). The main peak along the c-axis showed stronger intensity and narrower FWHM (Pic X:1,4 and 5) than the peaks taken at the angle of 30° and 50° to the main axis (Pic X: 2 and 3). The total number of Raman active modes for the diamond is one:

1T2g = 1. We expected that a strong electron-phonon coupling along the c-axis would cause stronger Raman scattering, resulting in an enhanced T2g vibration. Thus, we would get stronger intensity and narrower FWHM. Our assumption was justified. The portable Raman didn’t identify any signals responsible for treatment or colour modification. We conclude that our sample represents a naturally colourless, fully transparent diamond, free from impurities.

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6.3.1.2 Ruby (red corundum) We studied three samples of red corundum, ruby. One was from the Mineralogical collection of the Department of Earth Sciences and had big enough crystals (2-6 mm), each of which could be counted as unpolished gems. Two were borrowed from the Research Collection at the Department of the Earth Sciences and represented two small (2mm in diameter) spherical polished pink-red rubies, one originally from Switzerland and the second from the US. The portable Raman system identified three main peaks of the two small polished rubies, at -1 415, 642 and 1086 cm . These vibrations represent 1 A1g and 2 Eg modes. The FWHM fluctuates between 9 and 13 for the sample from Switzerland and between 10 and 14 for the sample from the US. This slight difference in FWHM can be explained by the slight difference in the concentration of Cr3+, whereas the sample from US has a higher concentration than the one from Switzerland. The portable Raman spectroscopy also showed that both samples are natural (non-synthetic) and untreated (their colour was not modified with the help of irradiation or heat treatment). The sample from the Mineralogical Collection at the Department of the Earth Sciences showed nine peaks in total at 258, 415, 442, 610, 1270, 1355, 1460, 1605, and 1622 cm-1. The -1 -1 peak at 415 cm represents A1g and the peak at 442 cm represents shifted Eg. We believe that the first peak at 258 cm-1, which is broad (FWHM= approx. 60), represents traces of natural heat treatment which could be caused by regional metamorphism or even by a radiation source. We assume that the rest of the peaks (610, 1270, 1355, 1460, 1605 and 1622 cm-1) represent fluorescence and impurities. Crystal Sleuth RRUFF search engine identified a 51% match with rutile, 51 % with corundum, 50% with zircon and 46% with quartz. The peak at 610 cm-1 can show the presence of rutile, while other peaks represent impurities which we could not identify. The presence of impurities is an evidence of structural disorder caused by dissolutions of zircon, rutile or calcite inclusions that are known to exist in natural corundum. We surmise that the presence of the quartz “fingerprint” is explained by the silica-rich matrix (grey-dark grey) in which crystals of red corundum were found. We discard the idea that there could be possible inclusions of quartz in the ruby lattice, because corundum recrystallizes during the contact with quartz to kyanite, sillimanite, andalusite: Al2O3 + SiO2 -> Al2SiO5 (Harlov & Newton, 1993).

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6.3.2 Semi-precious gemstones

6.3.2.1 Peridot (forsterite) The Raman spectra of the first peridot sample showed a well-developed doublet with positions that are characteristic for forsterite peaks: DB1 at 822.7 cm-1 and DB2 at 854.9 – -1 855.1 cm . Full width at half maximum (FWHM) for all peaks, especially for B1g, varies significantly. The wide range of FWHM along with the additional peak at 471.7 cm-1 implies that the mineral’s chemistry is “contaminated” with additional chemical element/elements. The comparative analysis with the RRUFF database confirms the assumption that forserite contains impurities. The Raman band showed a third small shoulder on the main doublet which is characteristic for RRUFF samples with impurities, e.g. sample with ID:R100100 (Figure 112). The Raman band of the second peridot sample also exhibited a well-developed doublet with separated DB1 at 822.1 – 822.4 cm-1 and DB2 at 854.6 – 854.8 cm-1. Full width at half maximum (FWHM) of the doublet does not diverge much, staying at range between 11.7 and

13.3 for both peaks. However, FWHM for B1g and B3g varies more significantly. B2g peaks are absent in both samples. The second sample of peridot also showed an additional peak at 296. 4- 296.9 cm-1. The second sample has a slightly developed third minor peak, the small shoulder of the doublet. The comparative analysis with RRUFF database and presence of the additional peak also point out that the second forstrerite contains impurities (Figure 113). The type of the third sample, olivine, was unknown before the experiment. The Raman scattering of the sample revealed that this is also a forsterite. The mineral showed a well- developed doublet with separate DB1 at 823.3 – 823.8 cm-1 and DB2 at 855.8 – 856.4 cm-1. Exactly as in the two previous cases, this sample exhibited a minor shoulder on the main doublet. Full width at half maximum (FWHM) for the doublet does not vary a lot: between

10.3 and 14.4 for both peaks. FWHM diverges more for B1g and B3g. The Raman band of this sample showed also the additional peak at 298. 7 – 300.9 cm-1, the same additional peak was registered during the experiment with the second peridot sample. The Raman band of the third sample is more alike the second one and the comparative analysis with the RRUFF database confirmed the presence of impurities in this sample too (Figure 114). We assume that the small minor third shoulder on the main doublet indicates the presence of Fe2+ in all three samples.

147

6.3.2.2 Azurite As it is discussed in the literature (Frost et al., 2002, Buzgar & Apopei, 2009), the main characteristic intensive peak for azurite is between 400 and 404 cm-1. While the main peak is just slightly shifted for the first sample (from 5 to 1 wavenumbers), the shift is significant for the second sample (between 60 to 61 wavenumbers). The presence of the various additional peaks along with shifted main peak points out that both samples contain impurities. The comparative analysis with RRUFF database did not give any results since RRUFF contains Raman spectra only of two azurite specimens with ideal chemistry. However, literature suggests (Aru et al., 2014) that the presence of broad peaks in the region of 1323 and 1590 cm-1 indicates the presence of carbon. The second azurite sample has both peaks which are characteristic for presence of carbon. The strongest additional peak of the second sample is the peak at 1244-1245 cm-1. This external vibration was most probably caused by the surrounding environment. In general, the portable Raman spectroscopy failed to show a range of peaks which are characteristic for azurite: ν4-Symmetric CO3 bending mode, O-H out-of-plane bending mode,

ν3-Asymmetric CO3 stretching mode, O-H bending mode and O-H stretching mode.

6.3.2.3 Fluorite As it was mentioned in the introduction part, our goal is to study the main fluorite peak, identified in literature as Stoke at 322 cm-1. Our hypothesis is that this peak’s intensity is directly dependent on the colour of the fluorite, i.e. on the incorporated elements in the crystal structure, such as metals, REE or even organic substances, which cause the colouring of the mineral. We studied 5 different varieties of the mineral: 3 blue, 2 purple, 1 white opaque, 1 colourless and 1 grey fluorite. What makes fluorite exhibit such wide range of colours? Or what makes us experience fluorite colour differently? The answer is electronic structure. Electronic transitions – excitations of electrons across energy levels - produce different colours, by absorbing, emitting or reflecting light differently. If the fluorite had an ideal crystal structure, free from vacancies and impurities and contains no other elements than Ca and F, it would appear transparently clear and colourless, letting all wavelengths of the light pass. However, atomic bonds between Ca and F can be destroyed by radioactive sources. This source can be rare earth elements, REE (with the exception of promethium, which is nonradioactive). Radioactive particle/radiation can cause a fluorine ion to be ejected from the crystal, creating a vacancy. In the moment when the crystal is missing one fluorine ion, the structure is no

148 longer electrically neutral, because it lacks one negative charge. To achieve stability, it attracts any free electron which happens to be close to the crystal and fills the vacancy by it. If the attracted electron were for example Fe4+ or Eu3+, it would give rise to a purple colour and create a “colour centre”. This “colour centre” would absorb energy in the form of photons in the yellow range of the spectrum and emit the purple range to get rid of the extra energy. If the missing fluorine ion were substituted by Al3+, the emitted light would exhibit grey colour (Geology and Earth Sciences News and Information, 2005). Sometimes the Ca ion becomes excited, and is thus ejected from the crystal system. In this case, it is also substituted by another element, for example by yttrium, which is responsible for the blue colour of fluorite (Geology and Earth Sciences News and Information, 2005). Fluorite has mostly a hydrothermal origin and is part of the gangue of metallic ore. It explains partly why the fluorite system can easily mobilize the missing metal ion to regain electric stability. Our experiment showed that blue fluorite fully misses the main peak at 322 cm-1. All peaks are concentrated in the area between 1100 and 1800 cm-1. They have also high FWHM, caused by different impurities. We believe that the presence of most probably yttrium is responsible for the damping effect of the Raman active band. We think that there is a need for further scientific investigation of the link between inactivation of the Raman band and the fluorite-yttrium atomic bond. Both purple and grey fluorites showed well-developed and easily recognizable main peaks at 318 cm-1. They have FWHM at 12-14, which is remarkably lower than width of other peaks. They are shifted by 4 cm-1 towards the lower numbers due to distortion in the lattice caused by the presence of either Fe4+ or any of REE ions, such as Eu3+. However, elements making fluorite purple do not cause a damping effect on the Raman active band. On the contrary, it appears, they enhance it, making it easily recognisable, even under high fluorescence, as in the case of fluorite 5. We cannot discuss our results of the white opaque fluorite and the transparent fluorite, because they showed to be calcites with a fluorite fingerprint. Fluorite can be associated with galena, sphalerite, barite, quartz, and calcite. Even the intergrowth between fluorite and calcite is not a rare phenomenon (Wenk & Bulakh, 2012). We believe that both samples were mistakenly identified as fluorite due to similarity in appearance and association with each other. The damping or enhancing effect on the only active Raman photon which gives a Stoke at 322 cm-1 should be more carefully studied. The knowledge of the mechanism behind this

149 effect can probably give new information about REE physical properties. It should also be added that our portable Raman system didn’t manage to identify REE. Burruss et al (1992) listed REE in the area between 400 and 750 nm, but we didn’t observe signals there.

6.4 Conclusions The biggest advantage of the portable Raman system is its relatively low cost, high analytical power and ease of use. Jewellery companies may find this method the most favourable, especially because it can perform unambiguous identification of minerals, inclusions and sometimes even determination of concentration of certain chemical elements in the crystal lattice. However, some inclusions can be a challenge for the portable system. The Raman spectroscopic system can identify the presence of diaspore fluid inclusions in a corundum. This ability is crucial since it gives a hint whether the corundum crystal was subjected to heat- treatment. The fact is that diaspore daughter crystals are decomposed below 1000°C in corundum. If the Raman system doesn’t identify the presence of diaspore, it can be an alarming indication that a gem has been heat-treated and all diaspore inclusions are gone (Dubessy et al., 2012). However, not all rubies contain diaspore. Our two samples (2mm spherical polished gems from the US and Switzerland) are inclusion-free, so an other analytical method had to be applied in order to justify whether the rubies were untreated. But we don’t discard the possibility that we could miss the presence of diaspore inclusions due to the small sample sizes and lower spatial resolution compared to the stationary Raman system, equipped with a high resolution microscope. Another important advantage of the portable Raman system is its mobility. It can be used on the national borders to control locomotion of the “politically branded” gems. Some gems come from poor parts of the world, where miners experience discrimination, pressure or where they can work in unsafe and hazardous conditions. The portable Raman system can identify a gem’s origin with the help of inclusions. For example, tourmaline and rutile needles in a blue sapphire would indicate that the gem comes from Kashmir, while diaspore inclusions are common for sapphires from Sri Lanka (Palanza et al, 2008). The portable Raman system can be an important socio-political instrument which can help to control legal and illegal movement of gems between borders. By all means, the most sensitive question is concerning “blood” or “conflict” diamonds. “Conflict diamonds” applies to situations where rebel movements are trying to destabilize legitimate authority and support their activities by trading the diamonds from the conflict area. It is forbidden to purchase “conflict diamonds” within the EU and many other countries

150 around the globe. However, Jeffrey Harris, an earth scientist at the University of Glasgow in Scotland, stated that “conflict diamonds” make up about 2.5% of the annual worldwide production. Other scientists have a more pessimistic view and estimate the conflict diamonds make up 4%, due to dark number of diamonds being smuggled outside of the “conflict diamond area” and entering the European market illegally (Global Policy Forum, 2009). Inclusions and tint play an important role in categorizing rubies and other corundum varieties. One obstacle to diamonds is that they are created under extreme conditions, making them naturally almost pure and virtually identical and can only be categorized by their inclusions (Dubessy et al., 2012). Another obstacle is that “conflict diamonds” reaching the European market have their defects and inclusions polished away, making it harder to identify their origin. Our diamond sample was inclusion-free and we could therefore not identify its provenance. But the technique of Raman spectroscopy is in a process of rapid development and we believe that soon one will be able to screen for “conflict diamonds” and eliminate them from the market. New technologies and social reforms will go hand in hand on the way to a more sustainable future.

7 Chapter III – Quartz family

7.1 Background Quartz belongs to the most extended mineralogical families in geology, the silica minerals.

The chemical composition of quartz is SiO2. At ambient pressure, quartz has two types of crystal systems: α-quartz, a trigonal low-temperature form, and β-quartz, a hexagonal high- temperature form. The Space Groups vary accordingly: P 3121 for the first crystal system and

P 3221 for the second one. The structure of quartz is simple: one silicon atom is coordinated 4- by four oxygen atoms, creating a tetrahedral SiO4 group (Figure 136). The bonds between silicon and oxygen are very strong, building a complex ionic-covalent structure. It makes quartz hard (Mohs scale:7) and resistant to weathering. The quartz tetrahedron is able to link to other tetrahedra in an infinite three-dimensional structure, by having two tetrahedra share one oxygen. This ability gives rise to a wide range of polymorphs and varieties. There are 25 different varieties, which are classified in 2 big groups: macrocrystalline and cryptocrystalline/microcrystalline. Macrocrystalline quartz builds well-defined crystals with an easily-observed structure. This type includes amethyst, citrine, smoky quartz, milky quartz, vermarine and others. Microcrystalline quartz forms one dense structure, where crystals are

151 not distinguishable from one another. Jasper, onyx, agate, chalcedony and others belong to this group (Wenk & Bulakh, 2012; The Quartz Page, 2005). Only the macrocrystalline group is studied in this work and it includes one transparent colourless quartz, one milky quartz, four smoky quartzes, three amethysts, three citrines and four rose quartz samples.

7.1.1 Pure colourless quartz Pure colourless inclusions-free quartz has 12 Raman active modes: 4A1 + 8E = 12.

Figure 136. Illustration of pure inclusions-free colourless quartz and its basic building block, SiO4 tetrahedron. Scientists have been interested in studying quartz with the help of Raman spectroscopy since the beginning of the 1960s. The main focus of the scientific investigations has been the question of residual stress trapped in the crystal structure and inclusions of quartz. The residual pressure or tensile stress expresses its presence through shift of peaks. Enami et al (2007) calculated the residual pressure with the help of Δω, which is a function of the standard sample difference in ω1 and ω2 between the α-quartz standard and the sample: Δω1= ω1 - ω1

sample standard. -1 -1 and Δω2 = ω2 -ω2 ω1 is the distance between A1 at 464 cm and A1 at 205 cm . ω2 -1 -1 is the distance between A1 at 205 cm and E at 127 cm . If the difference is positive, then the crystal retains residual pressure. If the difference is negative, then the crystal retains tensile stress. The higher the residual pressure, the bigger the difference of Δω1 and Δω2. The other widely discussed subject is the presence of coesite inclusions in the quartz lattice. Coesite is a quartz polymorph, which forms only in conditions of very high pressure (2-3 GPa) and relatively high temperature (700°C). The presence of coesite can reveal the geological history of the place, such as metamorphic processes or even meteorite collision

152 with the bedrock. Because the Raman spectroscopic studies of quartz have been going on for already 4-5 decades, the Raman active modes of quartz are well-known and established by hundreds of experiments. Scott & Porto (1967) and Ostroumov et al (2002) published their results with 35 years’ difference, but they match perfectly:

Table 88. Results of Raman spectroscopy applied to quartz. After Scott & Porto (1967) and Ostroumov et al (2002). N Raman active Ostroumov et al (2002): Raman band Scott & Porto (1967): Raman mode of quartz (cm-1) band of quartz (cm-1) 1 E 127 128

2 A1 205 207 3 E 264 265

4 A1 356 356 5 E 395 395

6 A1 464 464 7 E 695 695 8 E 795 795 9 E 806 807

10 A1 1082 1083 11 E 1162 1161 12 E 1230 1231

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Figure 137. Normalised RRUFF data on Raman scattering of colourless transparent quartz: R040031 (Source: Bob Downs, Locality: Spruce Claim, King County, Washington, USA), R100134 (Source: William W. Pinch, Locality: Sri Lanka), R150074 (Source: UAMM 9180, Locality: Selvino, Bergamo, Italy), R150091 (Source: Michael Scott, Locality: unknown). Table 89. Chemical composition of the RRUFF colorless quartz samples. ID Chemical composition Comments

R040031 Si1.00O2 Natural R100134 Unknown Natural R150074 Unknown Natural R150091 Unknown Natural

A semi-transparent-to-opaque, white-coloured macrocrystalline variety of quartz is called Milky quartz. The white colour is caused by numerous, evenly distributed inclusions of gas or liquid, trapped during crystallization (The Quartz Page, 2005).

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7.1.2 Smoky quartz

Figure 138. Illustration of the smoky quartz crystal system. A natural or artificial irradiation is needed for the transition of pure quartz to the smoky variety. For the sake of fact accuracy, it should be mentioned that the traces of aluminium, which are built into the crystal lattice, are also needed for the colour appearance (Figure 138). Si4+ gets excited due to the irradiation and leaves the crystal system, while Al3+ replaces the - empty silicon hole and forms an [AlO4] group. The replacement creates an imbalance of charge in the lattice, which is compensated for by incorporation of small monovalent cations + + + - (H , Li or Na ). The extra electron from the [AlO4] group is transferred to the cation, while H+, which is present outside of the system, interferes and enhances the process of colour centres formation in the crystal. The smoky colour can only appear after the crystal has formed, since temperatures above 50°C can destroy the colour centre. Therefore, it takes several million years for a crystal to launch a replacement reaction and the formation of colour centres linked with it (The Quartz Page, 2005). While the total number of the Raman active modes is 12, Fridrichova et al (2016) identified, in their recent work, 11 Raman active vibrations characteristic for the smoky variety (Table 89)

Table 90. Results of Raman spectroscopy applied to quartz. After Fridrichova et al (2016). Raman active mode Raman shift (cm-1) E 126 - 127

A1 205 – 206 E 260 – 263

A1 354 – 355

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E 394 – 400

A1 463

A2 501 – 508 E 695 – 696 E 806 – 807

A1 1079 – 1081 E 1157 - 1158

Figure 139. Raman spectrum of smoky quartz. Source: modified after Fridrichova et al (2016). The RRUFF database does not contain Raman spectra for smoky quartz. The main difference -1 between the smoky type and the pure type is the presence of the mode A2 at 501-508 cm and absence of E modes at 795 cm-1 and at 1230 cm-1.

7.1.3 Amethyst The best-known variety of quartz is violet-to-purple amethyst. Radioactive sources and the presence of iron, incorporated in the lattice, are prerequisites for the transformation from 3+ colourless quartz into purple amethyst (Figure 140). When Fe , incorporated in the SiO4 tetrahedron, is hit by gamma rays from a radioactive source, it loses one electron and forms

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Fe4+, an unusual oxidation state of iron (The Quartz Page, 2005). Later, Fe4+ is reduced to a Fe2+ and together with a Fe3+ creates a colour centre in the crystal. The reaction looks as - 3+ 0 2+ follows: [FeO4] + Fe → [FeO4] + Fe .

Figure 140. Illustration of the amethyst crystal system. Amethyst, as colourless quartz, has 12 Raman active modes. However, to identify all of them is a challenging task, thus, studies of synthetic amethyst are needed as a reference system (Figure 142, Table 90 and 91). It is also common to study amethyst along with other quartz varieties, such as citrine, smoky quartz or rose quartz (Figure 141).

Table 91. Dong et al. (2014) identified 8 Raman active modes among the 13 with the help of a portable Raman spectrometer, while Reiche et al (2004) distinguished 7 characteristic Raman vibrations. Raman Assignment Raman shift (cm-1) Raman shift (cm-1) active Dong et al. (2014) Reiche et al. (2004) mode Portable Raman Portable Raman E O–Si–O angle-bending vibrations Absent Absent

A1 O–Si–O angle-bending twisting 203 – 204 207 E O–Si–O angle-bending vibrations 260 – 261 260

A1 O–Si–O angle-bending vibrations 354 – 355 355 E O–Si–O angle-stretching vibrations 396 – 400 402- 405

A1 O–Si–O angle-bending vibrations 463 463

A2 O–Si–O angle-bending vibrations Absent 531 E O–Si–O angle-stretching vibrations 693-694 687 E O–Si–O angle-stretching vibrations Absent Absent

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A1 O–Si–O angle-stretching vibrations Absent Absent E O–Si–O angle-stretching vibrations 1157-1158 Absent

Figure 141. Raman spectra of light yellow citrine, purple amethyst and a reference Raman spectrum for quartz (RRUFFID=X080015, 780 nm). Modified after Dong et al. (2014).

Figure 142. Normalised RRUFF data on Raman scattering of amethyst: R060604 (Source: Michael Scott S100119, Locality: Piedras Parada, Veracruz, Mexico), R110104 (Source: Gemological Institute of America 10-

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12-2010-8, Locality: Synthetic), X080015 (Source: Gemological Institute of America 16730, Locality: Synthetic). Table 92. Chemical composition of RRUFF amethyst samples. ID Chemical composition Comments

R060604 Si1.00O2 Natural R110104 Unknown Synthetic X080015 Unknown Synthetic

7.1.4 Citrine Citrine is a pale yellow-to-brown variety of quartz. There are three main mechanisms which transform colourless quartz to citrine. The first one is related to the incorporation of Fe3+ into natural quartz crystals. Unlike amethyst, Fe3+ does not enter the crystal structure of citrine. It is mechanically incorporated during crystal growth, forming numerous non-structural tiny (200 nm diameter) impurities (Figure 143) (Balitsky & Balitskaya, 1986). The second type of transformation is associated with the presence of several hole centres adjacent to an aluminium impurity, along with an additional defect, but the exact nature of this defect is still unknown (Maschmeyer et al., 1980). The third type of transformation is related to radiation-induced colour centres, which are of non-impurity origin. These hole-like radiation-induced defects are due to a missing silicon or oxygen atom in the crystal system (Nilges et al., 2008).

Figure 143. Illustration of the citrine crystal system associated with the first mechanism of colour transformation.

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Citrine is reported to have a Raman band that is almost identical to the Raman band of amethyst (e.g. Dong et al., 2014; Jeršek et al., 2014; Petrova et al, 2012). RRUFF contains only one Raman spectrum of synthetic citrine, depicting 10 peaks (Figure 144).

Figure 144. Normalised RRUFF data on Raman scattering of citrine: X080016. Source: Gemological Institute of America 16730, Locality: Synthetic.

7.1.5 Rose quartz The interest of scientists to the mechanism that transforms colourless quartz to the rose variety rose early in 1910s. Early investigations did not shed light on this question, because analytical techniques at that time were simpler and less sophisticated. However, today’s advanced methods have not solved the problem completely either (Goreva et al., 2001; Clifford, 2012). Many different models have been proposed, but no consensus has been reached. Today, three main mechanisms are distinguished, which could take place in the transformation. The first mechanism is associated with the presence of Al3+ or Ti4+ (depending on the temperature of crystallization) in the quartz structure which substitute the missing Si, which in turn was knocked out of its position by heat or radiation (Figure 145). The second mechanism is related to the intervalence charge transfer (IVCT). IVCT is a charge transfer between pairs of ions, where they lose some of their electrical charge and transmit it to their neighbours. The process goes usually from a cation of lower oxidation state to a neighbouring cation of higher oxidation state. The third mechanism is associated with the presence of mineral inclusions and with the presence of a trace element incorporated in the crystal structure (Goreva et al., 2001; Clifford, 2012).

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Figure 145. Illustration of the rose quartz crystal system associated with the first mechanism of colour transformation. There is only one example of rose quartz Raman spectrum in the RRUFF database. It shows the standard quartz peaks with the strongest peak at 463 cm-1. This RRUFF sample is natural and pure, inclusions-free. It showed 11 peaks among 12 (Figure 146, Table 92):

Figure 146. Normalised RRUFF data on Raman scattering of rose quartz: R050125 (Source: Carlos and Paulo Vasconcelos, Locality: Linopolis, Minas Gerais, Brazil). Table 93. Chemical composition of RRUFF rose quartz. ID Chemical composition Comments

R050125 Si1.00O2 Natural

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7.1.6 Polishing agents There are 5 samples in total: one amethyst, two citrines, one smoky quartz and one rose quartz, which are cut and probably polished. A special covering could therefore have been applied for the polishing lustre effect. After a mineral is sawed and grounded, it is usually polished to a mirror-like reflection. Very fine grades of diamond (50,000 to 100,000 mesh) is a classical polishing agent, but there are many other, nowadays more popular and cheaper agents which can be used instead: aluminium oxide (alumina), cerium oxide, tin oxide, chromium oxide, ferric oxide (jeweler's rouge) or silicon dioxide (tripoli) (College of Natural Resources, US Berkeley, 2016). Thomas et al. (1989) reported that aluminium oxide gives 20 Raman active vibrations: 315, 335, 371 ,400, 414, 434, 440, 446, 501, 547, 559, 587, 591, 606, 652, 674, 719, 734, 745, 770 cm-1. Cerium oxide gives a strong vibration at 463 – 464 cm -1 (Wheeler & Khan, 2014). Tin oxide polish agent can show a very broad structure between 400 and 700 cm1 with an intense peak at around 576 cm1. This broad structure is the result of combination of various modes for

SnO2 (Vijayarangamuthu & Rath S, 2014). Li et al. (2012) studied iron oxide magnetic nanoparticles with the help of Raman spectroscopy. The scientist group identified 6 main Raman active vibrations at 219, 283, 398, 487, 604 and 1300 cm-1. Popovic et al (2011) noted that the silicon dioxide has a strong peak at 521 cm-1. The above-mentioned possible additional peaks, that may arise due to the presence of polishing agents, will be taken into consideration in the analysis.

7.2 Results

7.2.1 Colourless transparent quartz

Figure 147. Colourless, transparent quartz.

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An aggregate of 1-20 mm long crystals. The crystals are colourless, transparent, with vitreous lustre. Source: Mineral collection at the Department of Earth Sciences, shelf N 95, Uppsala University

Table 94. Raman spectroscopy results of the colourless transparent quartz. Raman Raman shift FWHM Peak shifts, Δω= ωstandard - ωsample Difference in Δω1 and active cm -1 (cm-1) Δω2 (after Enami et al, standard mode 2007): Δω1= ω1 - sample ω1 sample standard Δω2= ω2 – ω2 E 121.4 – 121.5 13.7 – 14.0 Shifted, 127 standard -121 sample =6 standard sample A1 200.7 – 201.8 27.4 – 28.3 Shifted, 205 -201 = 4 E 259.1 – 260.1 12.1 – 14.5 Shifted, 264standard – 260sample = 4 standard sample A1 350.8 – 351.4 10.7 – 15.0 Shifted, 356 – 351 = 5 E 394.1 – 396.4 12.1 – 26.6 Δω1 = 259.0 – (461.8 - E Absent Absent 200.7) = -2.1 cm-1 standard sample A1 461.3 – 461.8 12.9 – 13.0 Shifted, 464 – 462 = 2 Δω2 = (200.7 - 121.6) – E Absent Absent 77.8 = + 1.3 cm-1 E Absent Absent E Absent Absent

A1 Absent Absent E 1159.4 - 1159.7 11.2 – 14.6 Shifted, 1162standard – 1160sample = 2 E Absent Absent

The results of the experiment showed that all measured vibrations were shifted except for one, E at 395 cm-1. The calculation of the potential residual pressure or tensile stress showed that

Δω1= -2.1, while Δω2=+1.3. Despite the shift, the total distances of Δω1 and Δω2 and the correlation between them remain similar to the standard with a slight negative shift (approx. - 0.2), which points on the remnants of the residual stress (Figure 148).

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Figure 148. Comparison of Enami et al (2007) results of the calculations of residual pressure with the current study. Measurements of Enami et al (2007) match with the standard and are therefore comparable.

Figure 149. Normalised Raman bands of colourless transparent quartz.

7.2.2 Milky quartz

Figure 150. Milky quartz specimen. Description: a 10 cm long fraction of milky-white, opaque mineral. Crystal structure not recognisable. Dull lustre. Source: Mineral collection at the Department of Earth Sciences, shelf N 94, Uppsala University.

Table 95. Raman spectroscopy results of the milky quartz sample. N Raman Raman shit cm-1 FWHM Comments active mode 1 E 121.3 – 121.6 13.8 – 14.5 Shifted on 6 cm-1 -1 2 A1 200.6 – 200.8 27.3 – 28.7 Shifted on 5 cm

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3 E 258.5 – 259.7 12.1 – 14.5 Shifted on 5 cm-1 -1 4 A1 351.4 – 351.7 11.5 – 12.6 Shifted on 5 cm 5 E Absent Absent 6 E Absent Absent -1 7 A1 461.7 – 461.8 12.7 – 12.9 Shifted on 2 cm 8 E 694.7 – 695.4 4.1 – 6.5 Not shifted 9 E Absent Absent 10 E 807.0 – 807.8 8.8 – 14.0 Not shifted

11 A1 1080.6 – 1081.7 8.1 – 9.9 Not shifted 12 E 1158.0 – 1159.0 11.5 – 13.6 Shifted on 3 cm-1 13 E Absent Absent

Figure 151. Normalised Raman bands of milky quartz.

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7.2.3 Smoky quartz

7.2.3.1 Smoky quartz, 1

Figure 152. Smoky quartz, sample 1. Description: a 3-5 cm long polished smoky quartz of gem-quality. Source: Research collection at the Department of Earth Sciences, Uppsala University.

Table 96. Raman spectroscopy results of smoky quartz, sample 1. Raman active Raman shift (cm-1) FWHM mode E 121.6 – 121.7 13.8 – 13.9

A1 200.7 – 200.8 26.7 – 27.1 E 259.6 – 259.8 11.3 – 12.5

A1 351.2 – 351.8 10.5 – 12.5 E 393.7 – 394.9 15.4 – 17.8

A1 461.8 – 461.9 12.6

A2 Absent Absent E Absent Absent E 806.3 – 806.6 9.6 – 11.8

A1 1079.3 – 1080.3 7.7 – 10.8 E 1161.9 – 1162.2 25.1 – 26.2 Additional 1347.0 – 1347.5 22.6 – 27.6

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Figure X. Normalised Raman bands of smoky quartz 1.

7.2.3.2 Smoky quartz, 2

Figure 153. Smoky quartz, sample 2. Description: a flat, 5-7 cm long grey, translucent fragment of the mineral. Source: Mineral collection at the Department of Earth Sciences, shelf N 95, Uppsala University.

Table 97. Raman spectroscopy results of smoky quartz, sample 2. Raman active Raman shift (cm- FWHM mode 1) E 121.8 – 121.9 15.0 – 16.1

A1 201.5 – 201.7 33.1 – 34.0 E 258.9 – 259.5 11.8 – 12.5

A1 351.3 – 351.4 12.8 – 13.4 E 393.6 – 394.9 13.1 – 16.4

A1 461.6 13.6

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A2 500.4 – 500.8 10.0 – 12.0 E 693.4 – 694.6 8.6 – 19.6 E 800.2 – 800.8 22.1 – 24.0

A1 1080.0 – 1081.0 5.7 – 8.6 E 1161.1 – 1161.6 24.5 – 25.4 Additional 1346.4 – 1347.2 19.2 – 28.2

Figure 154. Normalised Raman bands of smoky quartz, sample 2.

7.2.3.3 Smoky quartz, 3

Figure 155. Smoky quartz, sample 3. Description: an aggregate of 1-2 cm long grey, translucent crystals. Source: Mineral collection at the Department of Earth Sciences, shelf N 95, Uppsala University.

Table 98. Raman spectroscopy results of smoky quartz, sample 3. 168

Raman active mode Raman shift (cm-1) FWHM E 121.3 – 121.4 14.0 – 14.1

A1 200.4 – 200.5 27.4 – 27.9 E 258.6 – 259.3 11.2 – 13.4

A1 350.9 – 351.4 11.4 – 14.8 E 391.8 – 392.0 12.3 – 12.9

A1 461.7 12.9 – 13.0

A2 Absent Absent E 693.2 – 694.1 10.9 – 13.7 E 796.6 – 797.3 15.9 – 17.7

A1 1064.0 – 1065.5 8.2 – 10.9 E 1159.4 – 1159.7 11.6 – 13.6 Additional 1883.6 15.4 – 18.8

Figure 156. Normalised Raman bands of smoky quartz, sample 3.

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7.2.3.4 Smoky quartz, 4

Figure 157. Smoky quartz, sample 4. Description: a 10-15 cm long grey, translucent fragment, broken. Source: Mineral collection at the department of Earth Sciences, shelf N 94, Uppsala University.

Table 99. Raman spectroscopy results of smoky quartz, sample 4. Raman active mode Raman shift (cm-1) FWHM E 121.3 – 121.4 14.2 – 14.5

A1 200.3 – 200.7 27.5 – 27.8 E 259.7 – 259.9 11.8 – 12.7

A1 351.2 – 351.3 11.6 – 11.9 E 394.5 – 395.2 16.1 – 20.5

A1 461.8 12.9 – 13.0

A2 Absent Absent E 694.3 – 694.4 12.6 – 13.8 E 807.3 – 807.4 10.5 – 10.9

A1 1080.7 – 1080.9 8.9 – 9.3 E 1158.6 – 1158.7 11.4 – 12.1

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Figure 158. Normalised Raman bands of smoky quartz, sample 4.

7.2.4 Amethyst

7.2.4.1 Amethyst 1

Figure 159. Amethyst, sample 1. Description: a 10-15 cm long grey, translucent fragment, broken. Source: Mineral collection at the Department of Earth Sciences, Uppsala University.

Table 100. Raman spectroscopy results of amethyst, sample 1. Raman active mode Raman shift cm -1 FWHM E 123.5 – 123.6 13.3 – 13.8

A1 202.2 – 202.4 27.0 – 28.6 E 260.8 – 261.1 10.9 – 11.6

A1 352.4 – 352.7 11.2 – 12.1 E 397.3 – 399.0 12.6 – 23.6 E Absent Absent

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A1 462.8 – 462.9 12.4 – 17.7 Additional 616.7 – 618.6 10.8 – 12.6 E 693.2 – 694.0 10.7 – 11.7 E 794.7 – 795.0 6.5 – 8.8 E 807.3 – 807.9 5.7 – 8.7 Additional 1002.3 – 1002.6 7.2 – 8.8 Additional 1065.3 – 1066.0 9.0 – 12.5

A1 1083.1 – 1084.1 8.0 – 9.5 E 1160.0 11.4 – 11.5 E Absent Absent

Figure 160. Normalised Raman bands of amethyst, sample 1.

7.2.4.2 Amethyst 2

Figure 161. Amethyst, sample 2.

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Description: a 10-15 cm long grey, translucent fragment, broken. Source: Mineral collection at the department of Earth Sciences, Uppsala University.

Table 101. Raman spectroscopy results of amethyst, sample 2. Raman active Raman shift cm -1 FWHM mode E 122.7 – 123.1 13.9 – 14.4

A1 201.6 – 201.8 27.2 – 28.0 E 260.2 – 260.8 11.9 – 12.9 Additional 316.3 – 317.1 5.7 – 10.6

A1 351.1 – 352.7 12.2 – 15.9 E 393.4 – 399.4 14.2 – 17.4 E Absent Absent

A1 461.1 – 462.4 12.9 – 13.0 Additional 552.4 – 552.9 8.7 – 16.1 E 692.7 11.4 E 794.4 9.8 E 806.8 – 808.8 5.7 – 9.1 Additional 1065.0 – 1066.7 3.5 – 16.8

A1 1081.0 – 1082.6 3.5 – 8.8 E 1159.2 – 1160.8 11.1 – 12.5 E Absent Absent

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Figure 162. Normalised Raman bands of amethyst, sample 2.

7.2.4.3 Amethyst 3

Figure 163. Amethyst, sample 3. Description: a 10-15 cm long grey, translucent fragment, broken. Source: Mineral collection at the Department of Earth Sciences, shelf N 95, Uppsala University.

Table 102. Raman spectroscopy results of amethyst, sample 3. Raman active Raman shift cm -1 FWHM mode E 122.2 – 122.7 12.4 – 13.4

A1 201.2 – 201.6 26.9 – 29.6 E 259.1 – 259.7 11.0 – 14.6 Additional 298.1 – 299.0 9.7 – 10.1 Additional 315.6 – 318.7 3.1 – 17.3

A1 351.8 – 352.4 10.8 – 16.5 Additional 368.0 12.8 E 392.5 – 396.3 3.8 – 16.8 E 411.8 – 414.2 5.5 – 7.0

A1 462.3 – 462.4 12.3 – 12.4 E 692.8 – 696.4 11.4 – 33.4 E 796.8 4.9 E 805.2 – 807.5 5.7 – 11.1

A1 Absent Absent E 1159.9 – 1160.8 7.6 – 14.5 E Absent Absent

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Figure 164. Normalised Raman bands of amethyst, sample 3.

7.2.5 Citrine

7.2.5.1 Citrine 1

Figure 165. Citrine, sample 1. Description: a 2-3 cm in diameter, spherical, transparent, pale yellow, polished of gem-quality mineral. Source: Research collection at the Department of Earth Sciences, Uppsala University.

Table 103. Raman spectroscopy results of citrine, sample 1. Raman active Raman shift cm -1 FWHM mode

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E 122.0 13.5 – 13.6

A1 201.2 26.9 – 27.0 E 259.5 – 259.6 11.4 – 12.1

A1 351.3 – 351.4 11.0 – 11.5 E 394.7 – 395.0 14.8 – 15.8 E Absent Absent

A1 462.2 12.3 – 12.4 Additional 532.6 - 533.1 8.1 – 8.5 E 694.6 11.6 – 12.0 E 799.6 – 799.7 18.5 – 19.8 E Absent Absent Additional 1064.8 – 1065.1 8.5 – 11.1

A1 1080.8 – 1081.6 5.3 – 6.8 E 1159.3 10.7 – 10.8 E 1231.8 – 1232.3 16.1 – 19.2

Figure 166. Normalised Raman bands of citrine, sample 1.

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7.2.5.2 Citrine 2

Figure 167. Citrine, sample 2. Description: a 1cm in diameter, transparent, pale yellow, polished of gem-quality mineral. Source: Research collection at the Department of Earth Sciences, Uppsala University.

Table 104. Raman spectroscopy results of citrine, sample 2. Raman active Raman shift cm -1 FWHM mode E 121.4 – 121.6 13.7 – 14.4

A1 200.4 – 200.8 27.2 – 27.9 E 259.4 – 259.9 11.7 – 12.7

A1 351.7 – 351.8 11.6 – 12.5 E 397.5 – 398.7 11.7 – 21.5 E 413.5 – 414.6 5.3

A1 461.9 – 462.0 12.7 – 12.9 E Absent Absent E Absent Absent E 806.4 – 807.2 7.2 – 8.0

A1 1081.6 – 1082.0 7.3 – 9.7 E 1154.9 – 1159.1 5.1 – 12.6 E Absent Absent

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Figure 168. Normalised Raman bands of citrine, sample 2.

7.2.5.3 Citrine 3

Figure 169. Citrine, sample 3. Description: a 2 cm long, semi-transparent, orange-yellow fragment. Source: Research collection at the Department of Earth Sciences, Uppsala University.

Table 105. Raman spectroscopy results of citrine, sample 3. Raman active Raman shift cm -1 FWHM mode E 121.2 – 121.4 13.7 – 14.4

A1 200.2 – 200.9 27.7 – 29.0 E 259.9 – 260.6 11.3 – 12.6 Additional 288.0 – 288.8 4.4 – 6.3 Additional 299.3 – 300.2 4.5 – 4.7

A1 351.5 – 352.0 11.3 – 15.5

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Additional 377.0 – 377.6 4.6 – 6.2 E 398.0 – 399.3 13.2 – 23.5 E 412.5 – 416.2 6.8 – 23.7

A1 461.7 – 461.9 12.9 E Absent Absent E Absent Absent E 807.1 – 807.6 7.2 – 8.1

A1 1081.5 – 1082.0 7.0 – 8.3 E 1158.1 – 1159.4 7.7 – 17.0 E Absent Absent Additional 1346.5 – 1346.9 5.0 – 5.3

Figure 170. Normalised Raman bands of citrine, sample 3.

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7.2.6 Rose quartz

7.2.6.1 Rose quartz 1

Figure 171. Rose quartz, sample 1. Description: an aggregate of 5-7 cm long reddish-pink, transparent crystals in white quartz matrix. Source: Mineral collection at the Department of Earth Sciences, shelf N 94, Uppsala University.

Table 106. Raman spectroscopy results of rose quartz, sample 1. Raman active Raman shift cm -1 FWHM mode E 121.5 – 122.2 13.7 – 14.2

A1 200.7 – 201.5 27.3 – 27.9 E 259.7 – 260.5 11.3 – 12.3

A1 351.5 – 352.2 11.0 – 11.2 E 390.7 – 393.1 14.7 – 27.0 E Absent Absent

A1 461.8 – 462.6 12.6 – 13.8 E 694.3 – 694.7 11.9 – 13.6 E Absent Absent E 807.2 – 807.8 10.1 – 11.6

A1 1081.0 – 1081.6 8.6 – 9.7 E 1159.2 – 1159.9 11.5 – 13.1 E 1229.4 – 1231.3 11.8 – 20.7

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Figure 172. Normalised Raman bands of rose quartz, sample 1.

7.2.6.2 Rose quartz 2

Figure 173. Rose quartz, sample 2. Description: a 5-6 cm long, half reddish-pink, half white, transparent quartz crystal. Source: Mineral collection at the Department of Earth Sciences, shelf N 95, Uppsala University.

Table 107. Raman spectroscopy results of rose quartz, sample 2. Raman active Raman shift cm -1 FWHM mode E 121.6 – 121.7 13.2 – 13.9

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A1 200.8 – 200.9 27.5 – 27.9 E 260.2 – 260.5 12.0 – 12.7

A1 351.7 – 352.2 10.7 – 11.6 E 397.8 – 399.2 13.7 – 29.0 E Absent Absent

A1 462.1 12.4 – 12.8 E 694.7 – 694.9 10.8 – 14.7 E Absent Absent E 807.6 – 807.8 10.3 – 11.3 Additional 1000.6 – 1001.3 7.5 – 8.9

A1 1080.9 – 1081.2 8.7 – 10.1 E 1158.3 – 1158.5 11.7 – 13.4 E 1228.9 – 1231.4 10.8 – 18.7 Additional 1324.6 – 1329.6 31.4 – 97.0 Additional 1596.9 – 1598.5 40.4 – 49.5 Additional 1601.2 -1601.8 2.8 – 15.7

Figure 174. Normalised Raman bands of rose quartz, sample 2.

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7.2.6.3 Rose quartz 3

Figure 175. Rose quartz, sample 3. Description: a 1-2 cm in diameter, spherical, semi-transparent, pink, polished of gem-quality mineral. Source: Research collection at the Department of Earth Sciences, Uppsala University.

Table 108. Raman spectroscopy results of rose quartz, sample 3. Raman active Raman shift cm -1 FWHM mode E 121.5 – 122.0 12.2 – 13.5

A1 200.9 – 202.0 27.1 – 36.4 E 261.4 – 262.2 12.3 – 13.8

A1 352.6 – 354.6 11.3 – 17.6 E Absent Absent E 399.2 – 400.0 10.0 – 14.4

A1 462.4 12.2 – 14.1 Additional 553.0 – 553.4 9.9 – 11.3 E Absent Absent E Absent Absent E 808.4 – 808.9 7.4 – 8.1

A1 1081.9 – 1082.1 7.1 – 7.8 E Absent Absent E Absent Absent Additional 1347.3 – 1347.7 4.8 – 5.7 Additional 1674.3 – 1675.7 8.5 – 21.5

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Figure 176. Normalised Raman bands of rose quartz, sample 3.

7.2.6.4 Rose quartz 4

Figure 177. Rose quartz, sample 4. Description: a 7-9 cm long, opaque, pink fragment. Source: Mineral collection at the Department of Earth Sciences, shelf N 95, Uppsala University.

Table 109. Raman spectroscopy results of rose quartz, sample 4. Raman active Raman shift cm -1 FWHM mode E 121.5 – 121.9 13.0 – 13.9

A1 200.3 – 200.9 26.4 – 29.4 E 259.6 – 260.3 11.8 – 12.2

A1 351.3 – 352.3 11.1 – 12.7 E 392.9 – 394.0 15.0 – 23.9 E Absent Absent

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A1 461.9 – 462.1 12.1 – 13.1 E Absent Absent E Absent Absent E 803.2 – 806.8 7.9 – 18.7

A1 Absent Absent E 1159.2 – 1160.9 12.1 – 13.8 E 1255.7 3.4

Figure 178. Normalised Raman bands of rose quartz, sample 4.

7.3 Discussion and conclusions

7.3.1 Pure and milky quartz Raman spectroscopy showed that both the colourless and milky quartzes have shifted vibrational bands. While the colourless quartz has all peaks shifted towards the lower numbers, milky quartz has 6 shifted peaks out of 13. The approach of Enami et al (2007) was demonstrated, where the residual pressure was calculated with the help of the difference in

Δω1 and Δω2. The calculation showed a negative result (-2.1 + 1.3 = -0.8), which means that the sample retains tensile stress, rather than compression. Despite that peaks are shifted in both quartz samples, especially the first five peaks (3E + 2A1) which play an essential role in

185 the residual pressure calculations, the possibility of instrumental failure is discarded, because the described method of Enami et al (2007) is advantageous and uses differences in peak positions within a given spectrum and, therefore, the effects of calibration errors (if any) are largely self-eliminated. The portable Raman was calibrated before the start of the experiment and did not show the same strong shift in other samples. Since the Raman bands of quartz have shifts, which are depended on pressure, it is possible to estimate the residual stress field. Using calculations of Liu and Mernagh (1992) and Schmidt and Ziemann (2000), the interval at which the tensile stress was applied is between 0.23 and 1.0 GPa (Figure 179).

Figure 179. Frequency shifts of the three most intense modes, 1A1, 2A1 and E, in the Raman spectrum of colourless, first sample of quartz as a function of pressure at room temperature. The frequency shifts are relative to the line positions at 0.1 MPa pressure. Modified after: dashed line - equation of Liu & Mernagh (1992) and solid lines – Schmidt & Ziemann (2000); red, blue and green stars represent this study. Ultimate tensile strength (UTS), a measure of the maximum stress that a material can withstand while being stretched or pulled before breaking, is 2.8 GPa for diamond (Abrosimov et al., 2015). UTS is significantly lower for quartz – it can vary beween 0.17 and 0.26 GPa and, theoretically, the crystal should break at the upper limit of the interval, 1 GPa (Harvey, 2005). However, scientists have registered even higher residual stress limits in the crystals of quartz. Masuda et al. (2011) used a triangular pyramidal diamond indenter in their experiment at a maximum load of 500 mN. This load produced a very small residual volume of less than 1 μm3, which made the quartz crystal highly stressed. Later they used Raman microspectroscopy to register shifts in the Raman bands, which would indicate a presence of

186 the residual stress field. The results of the experiment revealed that at the center of the indentation, the maximum compressive stress was higher than 2.2 GPa and the tensile stress was higher than 0.1 GPa.

7.3.2 Smoky quartz The first and the second smoky quartz samples showed a weak signal at 1347 cm-1, aside from the expected 13 Raman active vibrations. We know that the first sample was cut and polished to receive a gem quality, while we are not sure if the second smoky quartz sample had the same fate. However, we assume that both samples were polished by ferric oxide, which gives the weak signal. The third smoky quartz sample showed an additional weak signal at 1883.5 cm-1, which we classify as a signal of an inclusion. The fourth sample did not show any additional signals. It is transparent and does not exhibit visual defects. We believe that the fourth sample is free from impurities.

7.3.3 Amethyst and citrine Raman spectroscopy showed a medium signal at 1064-1066 cm-1 for the first amethyst sample (polished), for the second amethyst sample (polished) and for the first citrine sample (polished). We suggest that this signal belongs to the polishing agent. However, we are not sure of which nature. We identified an additional peak at 316-318 cm-1 for the second amethyst sample (polished) and the third amethyst sample (not polished). We think that this additional signal has nothing to do with the polishing agent, but rather express the common for the amethyst defect. The additional peak at 298-300 cm-1 was detected at the Raman spectrum of the third amethyst sample (not polished) and the third citrine sample (not polished). We suspect that this peak, which is common for both minerals, is evidence of the citrine having been heat treated and converted from amethyst. This sample has also an orange shade in its yellow, which can be considered indirect evidence of treatment, since converted amethyst usually exhibits orange-yellow colour, not pale-yellow, as natural citrine does (Balitsky & Balitskaya, 1986). The second amethyst sample (polished) and the third rose quartz sample (polished) showed an additional signal at 552-553 cm-1. We believe that this signal is linked to the presence of an aluminium oxide polishing agent. Thus, we imagine that the above-mentioned additional peak at 1064-1066 cm-1 could also be related to the same polishing agent.

187

7.3.4 Rose quartz The second sample of rose quartz (not polished) and the third sample of rose quartz (polished) showed additional signals at 1324, 1347, 1597, 1675 and 1601 cm-1. We surmise that these vibrations denote to the presence of impurities in the structure of both samples. The fourth sample did not show additional signals. We believe it is free from impurities. We did not manage to find clear Raman active vibrations, which would be characteristic of one or another quartz variety and which would help to distinguish them. Our experiment showed that macrocrystalline varieties of quartz have almost identical Raman bands. However, we demonstrated the possibility of the polishing agent identification along with identification of impurities and defects. There is a scarcity of scientific that covers and compares all main quartz varieties from the perspective of the Raman spectroscopy. Although such an investigation would be highly appreciated to further deepen the knowledge of crystallographic differences and geochemistry of the colour centres in the mineral lattices.

8 Chapter IV – Garnet family

8.1 Background Garnets are a large family of minerals, which are abundant in the Earth’s crust, upper mantle and transition zone. They can be formed in different geological environments and by different processes, such as magmatic, metamorphic and hydrothermal (Hofmeister and Chopelas, 1991; Gilg & Gast, 2016).

There are six common end-members of the garnet family: pyrope (Mg3Al2Si3O12), almandine (Fe3Al2Si3O12), spessartine (Mn3Al2Si3O12), grossular (Ca3Al2Si3O12), andradite

(Ca3Fe2Si3O12) and uvarovite (Ca3Cr2Si3O12) (Gilg & Gast, 2016). The general formula of the 2+ 3+ garnet group is X3 Y2 (SiO4)3. The first three end-members (pyrope, almandine and spessartine) belong to the pyralspite series, where Y is Al and X is either of Mg, Mn or divalent Fe. The other three end-members (uvarovite, grossular and andradite) belong to the ugrandite series, where X is Ca and Y is either of Cr, Al or trivalent Fe (Bersani et al., 2009). The garnet family has space group I a3d, and isometric-hexoctahedral crystal system (Mineralogy Database). The garnet chemical composition depends on P-T-X conditions during crystallization. Therefore, methods, based on P-T equilibria between garnets and other minerals, are useful tools for geothermobarometry (Gilg & Gast, 2016; Chopelas, 2005).

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8.1.1 Scientific background and what Raman spectroscopy can identify The first detailed Raman studies of garnet began 50 years ago, when garnets received important technological applications (Kolesov and Geiger, 1997; Moroz et al., 2009). Recent studies in Raman spectroscopy have provided a better understanding of the vibrational peculiarities in silicate structures. The garnet group is one of the most studied groups in Raman spectroscopy. The reason for this popularity is the fact that this group offers a complex, but excellent system to investigate the vibrational spectroscopic properties of silicate structures. This group has a complicated crystallographic structure, but high symmetry, which makes the analysis relatively simple. Besides, the big span in chemical composition between different end-members makes it perfect for studying correlation between Raman active vibrations and chemistry (Kolesov & Geiger, 1997). Raman spectroscopy is non-destructive and relatively cheap compared to microprobe analysis. Thus, one of the most discussed topics regarding investigations of garnets with the help of Raman spectroscopy is the possibility to determine chemical compositions of minerals. Determining the chemical composition of garnets has become an important task for scientists working in different fields, such as mineralogy or sedimentology, but also in gemmology and cultural heritage (Bersani et al., 2009). Gilg and Gast (2016) created a special technique which allows to quantify the amount of titanium content in pyrope by analysing a Raman band at 830 cm-1. Hofmeister and Chopelas (1991) studied 5 natural garnets with nearly end-member composition. The focus of their studies was thermodynamic properties of silicate garnets, such as heat capacity and entropy. The authors linked these thermodynamic properties with chemical composition, solving the problem of such a complex dependence with the help of Raman spectroscopy. Pinet and Smith (1994) worked on the correlation between various intense vibrations and chemical composition. This correlation showed quasi- linear trends. They identified a few spectra which only appeared when Ca was present. These peaks were observed in areas between 440 and 390 cm-1 and between 240 and 230 cm-1. The authors suggested that these peaks could be a marker for the presence of Ca in the lattice. Kolesov and Geiger (1998) were studying binary character of the Raman signals of crystals that had a mixed chemical composition. While working with crystals, which had a pyrope- grossular composition, they discovered that modes at 247 and 280 cm-1 strongly decreased in intensity as the content of grossular decreased. Thus, they linked these two peaks to the Ca translational motion, which could potentially help to identify the Ca content is garnets. Aside from work of Kolesov and Geiger (1998), the problem of the mixed chemical composition in garnets provoked a whole series of scientific investigations. As it is known, pure end- 189 members are very rare in nature. Most minerals have mixed compositions. Since natural garnet prefers to be either calcic or non-calcic (Merli et al., 1995), it is considered that garnets should be treated as bimodal, based on the calcium content in the X-site (Henderson, 2009). Moroz et al. (2009) studied garnets which were close to ugrandite in composition (a mixture between uvarovite, grossularite and andradite). The scientists’ aim was to investigate the relation between the Raman bands and the composition of the samples. They concluded that the identification of the chemical composition was only possible by Raman peaks analysis. They identified their samples as grossular–uvarovite solid solutions with high content of grossular and minor of uvarovite. Bersani et al. (2009) studied a series of standard garnets by Raman spectroscopy. All samples had a mixed chemical composition. Therefore, to identify the precise ratio of one mineral to another, the group of scientists used a special software which helped them obtain the molar composition of the garnets. The algorithm behind this software was based on the hypothesis that the different Raman active vibrations represented linear combinations of the end-members’ wavenumbers, weighted by their molar fraction. The authors plotted the chemical composition of the samples on the pyralspite and ugrandite garnets in triangle plots to illustrate the ratio of almandine-pyrope-spessartine for one group of samples and uvarovite-grossularite-andradite for another. The attempt to plot the results from the Raman spectroscopy analysis applied to garnets, using the method of Bersani et al (2009) is presented later in the discussion section of this report. Referring to the fact that the special software to obtain the chemical composition by Raman peaks analysis was not used in this work – rather manual calculation and estimation was used – it is important to mention that the possibility for error is higher. The question of the water content in garnets and possibility of water identification by Raman spectroscopy is also of interest. Arredondo and Rossman (2002) published their results with a conclusion that in the case with grossular, the correlation between additional Raman active signals and water content is clear. However, they failed to determine such a relation in the spessartine-almandine variety. Another not less important question which is often considered, is the presence and meaning of fluorescence bands. Makreski and Jovanovski (2008) identified two fluorescence peaks at 446 and 607 cm-1, which they assigned to the presence of rare-earth impurities in the sample of almandine. Moroz et al. (2009) faced also the problem of fluorescence background in 1500 – 3400 cm-1 regions, when they studied samples with the ugrandite chemical composition. This group also linked the fluorescence to possible rare earth elements in the composition of the minerals.

190

The behaviour of electrons in the garnet’s structure, when the mineral is subjected to different pressures, is also a widely-discussed question. It is an especially intriguing problem, because garnets are present in the upper mantle and in the transition zone, where pressures can reach 24 GPa (660 km). As the pressure increases, the chemical composition of garnets change. First, the garnet’s octahedral site, which usually incorporates Al, starts to accept Mg/Fe and Si, but not Ca. This makes clinopyroxene and orthopyroxene merge with the garnet, incorporating them as inclusions inside the garnet structure. The result of this process is called majorite, a mineral with the general formula (Mg,Fe)4Si4O12. But if pressure and temperature continue to grow (at depths greater than 660 km), the garnet transforms into

(Mg,Fe)(Al,Si)O3 perovskite (Frost, 2008). Studying inclusions in the garnet structure, in order to identify signs of the garnet having been subjected to pressure, can be time- consuming. Therefore, scientists have started to develop a new application of Raman spectroscopy, which could catch markers of pressure in the garnet’s wavenumbers and in the intensity of the peaks. Yan-Mei et al. (2006) studied how Raman spectra of pyrope changed with increasing pressure. They experimented up to 25.3 GPa, which corresponds to a depth even greater than the transition zone.

8.1.2 Raman spectroscopy of six main varieties of garnet

The total number of Raman active modes characteristic for the garnet group are 25: 3Ag1 +

8Eg + 14T2g (RRUFF). Some Raman active modes have similar characteristics. Hofmeister and Chopelas (1991) distinguished six common areas for all six end-members. The weak peak -1 1 (p1) is located between 980 and 1050 cm and is associated with the v3 (T2g+T1u) vibration. -1 The strong peak 2 (p2) is located between 870 and 920 cm and is linked to the v1 (A1g) -1 vibration. Peak 3 (p3) is usually situated between 810 and 870 cm and represents the v3 -1 (T2g+T1u) vibration. The weak peak 4 (p4) is located between 600 and 650 cm and is associated with the v4 (T2g+T1u) vibration. The moderate peak (p5), which represents the v2 -1 (A1g) vibration, is located between 510 and 560 cm . The highly intense peak 6 (p6) is linked -1 to the R(SiO4) (A1g) vibration and is located between 340 and 375 cm (Figure 180):

191

Figure 180. RRUFF Raman spectra of 6 main end-members of garnet: almandine, pyrope, spessartine, andradite, uvarovite and grossular. They have been normalized for peak intensity. The six peaks which are shown by dashed lines, illustrate the similarities between all 6 varieties and the shifted relationship to each other. They are grouped three and three to demonstrate the variations between calcic and non-calcic garnets.

8.1.2.1 Almandine, Fe3Al2Si3O12

Table 110. Raman modes of almandine. Symmetries Assignments Hofmeister & Kolesov & Geiger, Chopelas (1991) (1998)

T2g+T1u T(SiO4) mix 198 -

T2g T(SiO4) mix 239 -

T2g+T1u T(SiO4) 293 -

Eg T(SiO4) 326 256

Eg T(M) 163 171

T2g+T1u T(M) 166 170

T1u T(M) - 167

T2g+T1u T(M) 212 216

T1u T(Al) - -

T1u A(Al) - -

T2g+T1u R(SiO4) 312 314

A1g R(SiO4) 347 342

Eg R(SiO4) 368 323

T2g+T1u R(SiO4) 355 355

Eg V2 421 370

T2g+T1u V2 474 475

192

Eg V2 521 521

A1g V2 553 556

T2g+T1u V4 498 500

T2g+T1u V4 576 581

Eg V4 593 596

T2g+T1u V4 628 630

Eg V1 910 -

A1g V1 910 916

T2g+T1u V3 862 863

T2g+T1u V3 892 897

Eg V3 920 930

T2g+T1u V3 1032 1038

Figure 181. Normalised RRUFF data on Raman scattering of almandine: R040076 (Source: University of Arizona Mineral Museum 7976, Locality: Barton Garnet mine, Gore Mountain, Warren County, New York, USA), R040079 (Source: University of Arizona Mineral Museum 13736, Locality: Ontario, Canada), R040168 (Source: University of Arizona Mineral Museum 16323, Locality: Pocos Dos Cavatos, Ceara, Brazil), R050029 (Source: University of Arizona Mineral Museum 4307, Locality: Barton Garnet mine, Gore Mountain, Warren County, New York, USA), R060099 (Source: Roland Boehne, Locality: Alaska, USA), R050009 (Souce: George R. Rossman GRR-943, Locality: Riverside County, California, USA), X050010 (Source: George R. Rossman GRR-1056, Locality: Wrangel, Alaska, USA), X050011 (Source: George R. Rossman GRR-43, Locality: Rutherford #2 mine, Amelia, Virginia, USA). Table 111. Chemical composition of RRUFF Almandine samples. ID Chemical composition Comments

2+ R040076 (Fe 1.38Mg1.26Ca0.33Mn0.03)Σ=3Al2.00(Si1.00O4)3; trace Natural, mixed amounts of Ti

2+ R040079 (Fe 2.29Mg0.53Ca0.18)Σ=3Al2.00(Si1.00O4)3 Natural, mixed

2+ R040168 (Fe 1.48Mn1.47Ca0.05)Σ=3Al2.00(Si1.00O4)3; trace amounts Natural, mixed of Ti and Y

193

2+ R050029 (Fe 1.34Mg1.26Ca0.37Mn0.03)Σ=3Al2.00(Si1.00O4)3 Natural, mixed

2+ 3+ R060099 (Fe 1.63Mg0.57Mn0.56Ca0.24)Σ=3(Al1.98Fe 0.02)Σ=2(Si1.00O4)3 Natural, mixed

X050009 (Fe.684Mg.197Ca.061Mn.058)3Al2(SiO4)3 Natural, mixed

X050010 (Fe.559Mn.304Ca.101Mg.036)3Al2(SiO4)3 Natural, mixed

2+ 3+ X050011 (Fe 1.63Mg0.57Mn0.56Ca0.24)Σ=3(Al1.98Fe 0.02)Σ=2(Si1.00O4)3 Natural, mixed

8.1.2.2 Pyrope, Mg3Al2Si3O12

Table 112. Raman modes of pyrope. Symmetries Assignments Hofmeister and Kolesov & Geiger, Yan-Mei et al., Chopelas (1991) (1998) (2006)

T2g+T1u T(SiO4) mix 230 135 -

T2g T(SiO4) mix 285 222 -

T2g+T1u T(SiO4) 318 322 320

Eg T(SiO4) 342 284 -

Eg T(M) 203 211 208

T2g+T1u T(M) 208 - -

T1u T(M) - - -

T2g+T1u T(M) 272 - -

T1u T(Al) - - -

T1u A(Al) - - -

T2g+T1u R(SiO4) 350 353 -

A1g R(SiO4) 362 354 -

Eg R(SiO4) 365 344 365

T2g+T1u R(SiO4) 379 383 380

Eg V2 439 375 -

T2g+T1u V2 490 492 -

Eg V2 524 525 -

A1g V2 562 563 563

T2g+T1u V4 510 512 -

T2g+T1u V4 598 598 -

Eg V4 626 626 -

T2g+T1u V4 648 650 648

Eg V1 911 - -

194

A1g V1 925 928 925

T2g+T1u V3 866 871 867

T2g+T1u V3 899 902 900

Eg V3 938 945 -

T2g+T1u V3 1062 1066 1062

Figure 182. Normalised RRUFF data on Raman scattering of pyrope: R040159 (Source: University of Arizona Mineral Museum 4309, Locality: Meronitz, Bohemia), R050112 (Source: Carlos and Paulo Vasconcelos, Locality: Cruzeiro mine, San Jose, Minas Gerais, Brazil), R050113 (Source: Farooq and Nazia Sawal, Locality: Warsik, Pakistan), R060441 (Source: Gemological Institute of America 20594, Locality: Apache County, Arizona, USA), X050130 (Source: G.R. Rossman 1728, Locality: San Bernardo, Dora Maria Massif, Italy), X050190 (Source: G.R. Rossman 59b, Locality: Tanzania). Table 113. Chemical composition of RRUFF Pyrope samples. ID Chemical composition Comments

2+ R040159 (Mg2.17Fe 0.47Ca0.34Mn0.02)Σ=3(Al1.86Cr0.11Ti0.03)Σ=2((Si0.99Al0.01)Σ=1O4)3; Natural, mixed trace amounts of Rb?

2+ 3+ R050112 (Mg1.49Fe 1.18Ca0.29Mn0.04)Σ=3(Al1.99Fe 0.01)Σ=2(Si1.00O4)3 Natural, mixed

R050113 Natural, mixed 2+ 3+ (Mg1.83Fe 1.12Ca0.03Mn0.02)Σ=3(Al1.82Fe 0.18)Σ=2((Si0.99Al0.01)Σ=1O4)3

R060441 (Mg1.83Fe0.75Ca0.39Mn0.03)Σ=3(Al1.95Cr0.05)Σ=2(Si1.00O4)3 Natural, mixed X050130 Unknown

X050190 (Mg.603Fe.377Ca.013Mn.007)3Al2(SiO4)3 Natural, mixed

195

8.1.2.3 Spessartine, Mn3Al2Si3O12

Table 114. Raman modes of spessartine. Symmetries Assignments Hofmeister and Kolesov & Geiger, Chopelas (1991) (1998)

T2g+T1u T(SiO4) mix 194 196

T2g T(SiO4) mix 229 221

T2g+T1u T(SiO4) 300 -

Eg T(SiO4) 318 321

Eg T(M) 162 162

T2g+T1u T(M) 173 175

T1u T(M) - -

T2g+T1u T(M) 220 -

T1u T(Al) - -

T1u A(Al) - -

T2g+T1u R(SiO4) 314 302

A1g R(SiO4) 347 350

Eg R(SiO4) 372 372

T2g+T1u R(SiO4) 350 350

Eg V2 410 -

T2g+T1u V2 472 475

Eg V2 521 522

A1g V2 550 552

T2g+T1u V4 499 500

T2g+T1u V4 573 573

Eg V4 592 592

T2g+T1u V4 628 630

Eg V1 892 -

A1g V1 905 905

T2g+T1u V3 849 849

T2g+T1u V3 878 879

Eg V3 913 913

T2g+T1u V3 1027 1029

196

Figure 183. Normalised RRUFF data on Raman scattering of spessartine: R050063 (Source: Rock Currier, Locality: Fujian Province, China), R060451 (Source: Gemological Institute of America 11817, Locality: unknown), R080053 (Source: www.multicolour.com, Locality: East Africa), X050147 (Source: R2G 10, Locality: Rutherford #2 mine, Amelia, Virginia, USA), X050148 (Source: G.R. Rossman 72, Locality: Brazil), X050191 (Source: G.R. Rossman 61, Brazil) Table 115. Chemical composition of RRUFF Spessartine samples ID Chemical composition Comments

3+ R050063 (Mn2.72Fe0.24Ca0.04)Σ=3(Al1.95Fe 0.05)Σ=2(Si1.00O4)2.75(F0.58(OH)0.42)Σ=1; Natural, mixed trace amounts of Mg; OH estimated by charge balance

2+ R060451 (Mn1.26Mg0.98Fe 0.39Ca0.37)Σ=3Al2.00(Si1.00O4)3; trace amounts of Ti Natural, mixed

2+ 2+ 3+ 2+ R080053 (Mn 1.32Mg0.96Fe 0.38Fe 0.04)Σ=3Al2.00((Si2.96Al0.04)Σ=1O4)3; Fe and Natural, mixed Fe3+ splitted by charge balance

X050147 (Mn.921Fe.053Ca.025)3Al2(SiO4)3 Natural, mixed X050148 Unknown

X050191 (Mn.527Fe.469Ca.007)3Al2(SiO4)3 Natural, mixed

8.1.2.4 Grossular, Ca3Al2Si3O12

Table 116. Raman modes of grossular. Symmetries Assignments Hofmeister and Kolesov & Chopelas (1991) Geiger, (1998)

T2g+T1u T(SiO4) mix 238 247

T2g T(SiO4) mix 278 280

T2g+T1u T(SiO4) 330 333

Eg T(SiO4) 317 319

Eg T(M) 178 181

197

T2g+T1u T(M) 178 186

T1u T(M) - -

T2g+T1u T(M) 246 -

T1u T(Al) - -

T1u A(Al) - -

T2g+T1u R(SiO4) 349 351

A1g R(SiO4) 374 376

Eg R(SiO4) 369 373

T2g+T1u R(SiO4) 383 389

Eg V2 416 420

T2g+T1u V2 478 483

Eg V2 526 529

A1g V2 549 550

T2g+T1u V4 509 512

T2g+T1u V4 577 582

Eg V4 590 592

T2g+T1u V4 629 630

Eg V1 852 -

A1g V1 881 880

T2g+T1u V3 826 827

T2g+T1u V3 850 848

Eg V3 904 904

T2g+T1u V3 1007 1007

198

Figure 184. Normalised RRUFF data on Raman scattering of grossular: R040065 (Source: University of Arizona Mineral Museum 11764, Locality: Feng Tien mine, Taiwan), R040066 (Source: University of Arizona Mineral Museum 7979, Locality: Redding, Connecticut, USA), R050036 (Source: Eugene Schlepp, Locality: Wah Wah Mountains, Utah, USA), R050081 (Source: Rock Currier, Locality: Kayes Region, Mali), R050312 (Source: Eugene Schlepp, Locality: Eden Mills mine, Vermont, USA), R060382 (Source: Herb Obodda 041, Locality: Lalatema, near Mount Kilimanjaro, Tanzania). Table 117. Chemical composition of RRUFF Grossular samples. ID Chemical composition Comments

2+ 3+ R040065 (Ca2.90Fe 0.05Mn0.05)Σ=3(Al1.95Fe 0.03Ti0.02)Σ=2((Si0.99Al0.01)Σ=1O4)3 Natural, mixed

2+ 3+ R040066 (Ca2.90Fe 0.08Mn0.02)Σ=3(Al1.87Fe 0.13)Σ=2(Si1.00O4)3 Natural, mixed

3+ R050036 (Ca2.95Mg0.05)Σ=3(Al1.70Fe 0.30)Σ=2(Si1.00O4)3; trace amounts of Natural, mixed P

3+ R050081 (Ca2.92Mg0.07Mn0.01)Σ=3(Al1.04Fe 0.89Ti0.07)Σ=2((Si0.98Al0.02)Σ=1O4)3; Natural, mixed trace amounts of Y

3+ R050312 Ca3.00(Al1.75Fe 0.23Ti0.02)Σ=2((Si0.99Al0.01)Σ=1O4)3 Natural, mixed

R060382 (Ca2.95Mg0.03Mn0.02)Σ=3Al2.00((Si0.99Ti0.01)Σ=1O4)3; trace amounts Natural, mixed of Fe

8.1.2.5 Uvarovite, Ca3Cr2Si3O12

Table 118. Raman modes of uvarovite. Symmetries Assignments Kolesov & Chopelas (2005) Geiger, (1998

T2g+T1u T(SiO4) mix 242 237

T2g T(SiO4) mix 272 271

T2g+T1u T(SiO4) 178 330

Eg T(SiO4) 176 178

Eg T(M) - 325

T2g+T1u T(M) - 338

T1u T(M) - -

T2g+T1u T(M) 388 377

T1u T(Al) - -

T1u A(Al) - -

T2g+T1u R(SiO4) 459 -

A1g R(SiO4) 370 365

Eg R(SiO4) 366 365

T2g+T1u R(SiO4) - 453

Eg V2 - 390

T2g+T1u V2 509 497

Eg V2 526 508

199

A1g V2 526 519

T2g+T1u V4 - -

T2g+T1u V4 - 551

Eg V4 590 588

T2g+T1u V4 618 618

Eg V1 - -

A1g V1 876 878

T2g+T1u V3 838 837

T2g+T1u V3 864 864

Eg V3 894 892

T2g+T1u V3 1002 1000

Figure 185. Normalised RRUFF data on Raman scattering of uvarovite: R060477 (Source: Michael Scott S100206, Locality: Saranovskiy mine, Sarany, Ural Mountains, Russia), R061041 (Source: Royal Ontario Museum M52536, Locality: Outokumpu, Finland) Table 119. Chemical composition of RRUFF Uvarovite samples. ID Chemical composition Comments

R060477 Ca3.00(Cr1.15Al0.82Ti0.03)Σ=2((Si0.99Al0.01)Σ=1O4)3 Natural, mixed

3+ R061041 (Ca2.93Mg0.05Mn0.01 0.01)Σ=3.00(Cr1.23Al0.72Fe 0.03Ti0.02)Σ=2(Si1.00O4)3 Natural, mixed

8.1.2.6 Andradite, Ca3Fe2Si3O12

Table 120. Raman modes of andradite. Symmetries Assignments Hofmeister and Kolesov & Chopelas (1991) Geiger, (1998

T2g+T1u T(SiO4) mix 229 236

200

T2g T(SiO4) mix 264 264

T2g+T1u T(SiO4) 311 312

Eg T(SiO4) 296 174

Eg T(M) 173 174

T2g+T1u T(M) 173 -

T1u T(M) - -

T2g+T1u T(M) 235 289

T1u T(Al) - -

T1u A(Al) - -

T2g+T1u R(SiO4) 325 325

A1g R(SiO4) 370 370

Eg R(SiO4) 370 -

T2g+T1u R(SiO4) 382 382

Eg V2 352 352

T2g+T1u V2 452 452

Eg V2 494 492

A1g V2 516 516

T2g+T1u V4 494 494

T2g+T1u V4 553 553

Eg V4 576 574

T2g+T1u V4 593 593

Eg V1 843 -

A1g V1 872 -

T2g+T1u V3 816 816

T2g+T1u V3 842 842

Eg V3 874 874

T2g+T1u V3 995 995

201

Figure 186. Normalised RRUFF data on Raman scattering of andradite: R040001 (Source: University of Arizona Mineral Museum 12923, Locality: Stanley Butte, Graham County, Arizona, USA), R050256 (Source: Marcus Origlieri, Locality: Franklin, Sussex County, New Jersey, USA), R050311 (Source: Eugene Schlepp, Locality: Calaveras County, California, USA), R050377 (Source: University of Arizona Mineral Museum 2983, Locality: Zlatoust District, South Urals, Russia), R060350 (Source: Michael Scott S100023, Locality: south of the Gem mine, southern San Benito County, California, USA), R060358 (Source: Herb Obodda 010, Locality: Soghan, near Jiroft, Kerman, Iran). Table 121. Chemical composition of RRUFF Andradite samples. ID Chemical composition Comments R040001 Natural, mixed

Ca3.00(Fe1.96Al0.04)Σ=2(SiO4)3 ; trace amounts of Mn

3+ R050256 (Ca2.27Mn0.73)Σ=3(Fe 1.35Al0.65)Σ=2(Si1.00O4)3 Natural, mixed

2+ 3+ R050311 (Ca2.88Mn0.07Fe 0.05)Σ=3(Fe 1.39Al0.59Ti0.02)Σ=2((Si0.99Al0.01)Σ=1O4)3 Natural, mixed

3+ R050377 Ca3.00(Fe 1.48Ti0.31Mg0.14Zr0.07)Σ=2(Si2.73Al0.24Ti0.03)Σ=3O12 Natural, mixed

3+ 3+ R060350 (Ca2.93Mg0.07)Σ=3(Fe 1.18Ti0.77Al0.05)Σ=2((Si0.74Fe 0.26)Σ=1O4)3 ; Natural, mixed trace amounts of Mn

3+ R060358 Ca3.00(Fe 1.89Cr0.11)Σ=2(Si1.00O4)3 Natural, mixed

8.2 Result

202

Figure 187. Garnet specimens. Locality: Mineralogical Collection at the Department of Earth Sciences, shelves 59 and 60, Uppsala University. Eight different samples have been chosen for the Raman spectroscopy analysis.

8.2.1 Garnet 1

Figure 188. Garnet, sample 1. Description: dark red-brown, 3-5 cm long rhombic crystal. Locality: Mineralogical Collection at the Department of the Earth Sciences, Uppsala University.

Table 122. Raman modes of the first garnet sample. N Symmetry Raman shift cm-1 FWHM 1 Additional 135.2 - 136.1 1.9 - 10.6 2 Additional 146.1 - 151.9 4.5 - 12.7

3 T2g+T1u 172.3 - 174.0 12.9 - 15.8

4 T2g+T1u 236.9 - 241.2 5.8 - 23.3

5 T2g 273.4 - 274.3 14.8 - 22.1

6 Eg 321.6 - 323.1 6.1 - 12.8

7 Eg 367.4 - 367.7 19.1 - 20.6

8 Eg 405.8 - 410.9 13.9 - 21.8

9 Eg 539.3 - 539.7 11.2 - 13.1

10 T2g+T1u 622.9 - 624.4 9.9 - 32.5

11 T2g+T1u 822.0 - 822.5 20.6 - 22.8

12 A1g 878.2 - 878.4 16.1 - 16.7

13 T2g+T1u 1001.4 - 1003.8 8.3 - 17.0 14 Additional 1085.3 - 1085.5 5.6 - 6.7

CrystalSleuth identified an 84% match with majorite, only 42% match with pyrope, 40% match with spessartine. Higher matches were identified with Ca-garnets: 57% uvarovite, 53 % andradite and 59% grossular.

203

Figure 189. Comparison between the first garnet sample and the RRUFF grossular

8.2.2 Garnet 2

Figure 190. Garnet, sample 2. Description: dark red, 5-7 cm long rhombic crystal. Locality: Mineralogical Collection at the Department of the Earth Sciences, Uppsala University.

Table 123. Raman modes of the second garnet sample. N Symmetry Raman shift cm-1 FWHM

1 Eg 161.3 - 163.6 4.4 - 18.5

2 T2g+T1u 210.8 - 339.0 14.0 - 18.0

3 A1g 339.6 - 368.0 12.9 - 15.7

4 Eg 368.2 - 495.2 11.0 - 25.8

5 T2g+T1u 496.1 - 914.4 12.6 - 15.2

6 T2g+T1u 553.0 - 1034.2 5.5 - 30.9

7 Eg 914.6 - 914.7 15.2 - 15.5

8 T2g+T1u 1035.5 - 1038.4 21.6 - 32.2

204

Figure 191. Comparison between the second garnet sample and the RRUFF Almandine CrystalSleuth identified 83% match with majorite, 54% with grossular, 53% with pyrope, 52% with spessartine, 52% with almandine, and 51% match with uvarovite.

8.2.3 Garnet 3

Figure 192. Garnet, sample 3. Description: dark red, 0.5-1.5 cm long cubic crystals in sedimentary matrix. Locality: Mineralogical Collection at the Department of the Earth Sciences, Uppsala University.

Table 124. Raman modes of the 3rd garnet sample. N Symmetry Raman shift cm-1 FWHM 1 Additional: calcite 149.4 - 150.0 17.7 - 18.1 matrix

2 Eg 172.1 - 174.6 10.0 - 24.6

3 T2g+T1u 236.5 - 237.7 16.0 - 20.1

205

4 T2g+T1u 270.9 - 275.8 14.1 - 23.5

5 Eg 367.4 - 368.5 18.6 - 24.9

6 T2g+T1u 405.4 - 406.5 11.0 - 12.9

7 Eg 538.0 - 538.8 11.7 - 12.4

8 T2g+T1u 620.6 - 622.4 9.1 - 21.8 9 Additional: calcite 711.1 - 711.6 8.2 - 9.7 matrix

10 T2g+T1u 821.5 - 821.8 21.2 - 23.1

11 A1g 877.7 - 877.9 16.1 - 16.6

12 T2g+T1u 989.6 - 1002.4 5.0 - 13.1 13 Additional: calcite 1085.4 - 1085.6 6.1 - 6.2 matrix 14 Additional 1125.1 - 1126.3 17.8 - 26.7 15 Additional 1319.3 - 1322.5 3.9 - 19.8 16 Additional 1367.7 - 1370.1 4.7 - 33.7 17 Additional: calcite 1490.5 - 1491.4 18.7 - 22.6 matrix 18 Additional 1547.6 - 1548.4 14.0 - 18.4 19 Additional 1572.1 - 1575.7 13.8 - 31.3

Figure 193. Comparison between the 3rd garnet sample and the RRUFF Grossular and Andradite. CrystalSleuth identified a 61% match with andradite and a 63% match with grossular. The search engine did not identify a match with other garnet members.

206

8.2.4 Garnet 4

Figure 194. Garnet, sample 4. Description: dark red,3-7 cm long broken fragments in dark grey matrix. Locality: Mineralogical Collection at the Department of the Earth Sciences, Uppsala University.

Table 125. Raman modes of the 4th garnet sample. N Symmetry Raman shift cm-1 FWHM

1 Eg 173.3 - 174.3 13.3 - 19.7

2 T2g+T1u 238.7 - 239.5 15.0 - 24.5

3 T2g 272.0 - 274.9 10.7 - 20.8

4 Eg 322.2 - 325.4 9.3 - 22.2

5 Eg 369.0 - 369.6 15.33 - 22.3

6 Eg 407.3 - 408.3 9.6 - 15.2

7 A1g 540.8 - 542.6 9.1 - 11.6

8 T2g+T1u 622.0 - 624.4 6.5 - 31.6

9 T2g+T1u 823.2 - 824.4 18.7 - 21.4

10 A1g 878.9 - 879.2 15.5 - 15.9

11 T2g+T1u 1003.2 - 1005.6 5.6 - 24.9 12 Additional 1288.6 - 1292.8 4.5 - 6.6 13 Additional 1419.5 - 1419.7 5.6 - 45.9

207

Figure 195. Comparison between the 4th garnet sample and the RRUFF Grossular CrystalSleuth identified an 83% match with majorite, 62% with grossular and 62% with andradite.

8.2.5 Garnet 5

Figure 196. Garnet, sample 5. Description: dark red,3-7 cm long broken fragments in dark grey matrix + quartz. Locality: Mineralogical Collection at the Department of the Earth Sciences, Uppsala University.

Table 126. Raman modes of the 5th garnet sample. N Symmetry Raman shift cm-1 FWHM

1 Eg 173.2 - 175.2 12.4 - 14.7

2 T2g+T1u 238.1 - 239.1 14.2 - 23.2

3 T2g 272.6 - 275.2 14.2 - 28.5

4 Eg 321.4 - 322.4 6.3 - 20.6

5 Eg 368.6 - 369.9 15.8 - 26.5

6 Eg 406.0 - 407.3 11.4 - 17.5

208

7 Eg 495.0 - 497.5 2.6 - 4.6

8 A1g 539.3 - 539.4 10.5 - 13.1

9 T2g+T1u 621.1 - 637.6 5.0 - 11.4

10 T2g+T1u 822.8 - 824.4 20.5 - 22.2

11 A1g 879.1 - 879.3 15.8 - 16.4

12 T2g+T1u 1000.4 - 1003.6 2.0 - 23.2 13 Additional 1085.5 - 1086.1 5.8 - 6.8

Figure 197. Comparison between the 5th garnet sample and the RRUFF Grossular CrystalSleuth identified an 81% match with majorite, 70% match with grossular, 67% with uvarovite, and 67% with andradite.

8.2.6 Garnet 6

Figure 198. Garnet, sample 6.

209

Description: dark red,1-3 cm long rhombic crystal in light dark grey, gneiss-like matrix. Locality: Mineralogical Collection at the Department of the Earth Sciences, Uppsala University.

Table 127. Raman modes of the 6th garnet sample. N Symmetry Raman shift cm-1 FWHM 1 Additional 120.8 - 124.5 9.4 - 17.0 2 Additional 151.7 - 158.4 7.8 - 10.4

3 T2g+T1u 199.7 - 204.3 5.7 - 21.7

4 A1g 347.0 - 348.3 16.6 - 21.1

5 T2g+T1u 462.5 - 463.4 10.9 - 18.1

6 T2g+T1u 497.7 - 501.1 11.2 - 14.8

7 A1g 553.6 - 557.4 4.5 - 26.2

8 T2g+T1u 604.3 - 607.8 4.7 - 13.4

9 Eg 912.3 - 912.9 15.2 - 16.5

10 T2g+T1u 1034.2 - 1035.7 4.5 - 14.0

CrystalSleuth did not show any reasonable match.

Figure 199. Comparison between the 6th garnet sample and the RRUFF Almandine

210

8.2.7 Garnet 7

Figure 200. Garnet, sample 7. Description: dark red,1.5 cm long rhombic crystal in light dark grey, quartz-rich matrix. Locality: Mineralogical Collection at the Department of the Earth Sciences, Uppsala University.

Table 128. Raman modes of the 7th garnet sample. N Symmetry Raman shift cm-1 FWHM

1 Eg 160.9 - 162.3 11.3 - 21.6

2 T2g+T1u 210.2 - 214.4 2.8 - 27.3

3 A1g 339.9 - 340.5 13.3 - 20.0

4 Eg 366.9 - 369.1 10.2 - 25.3

5 T2g+T1u 495.6 - 496.8 11.2 - 18.4

6 A1g 552.7 - 554.4 16.2 - 25.7

7 Eg 915.1 - 921.4 13.5 - 20.4

8 T2g+T1u 1036.4 - 1037.8 9.4 - 25.5

211

Figure 201. Comparison between the 7th garnet sample and the RRUFF Almandine CrystalSleuth identified a 63% match with almandine, 63% match with pyrope and 58% match with spessartine.

8.2.8 Garnet 8

Figure 202. Garnet, sample 8. Description: red, 0.2-0.5 cm long rhombic crystals in green, mafic/ultramafic matrix. Locality: Mineralogical Collection at the Department of the Earth Sciences, Uppsala University.

Table 129. Raman modes of the 8th garnet sample. N Symmetry Wavenumber FWHM

1 T2g+T1u 1032.0 - 1037.9 5.2 - 71.8 2 Additional: carbon 1260.4 - 1265.4 10.1 - 53.5 3 Additional: carbon 1385.0 - 1385.0 16.9 - 18.0 4 Additional: carbon 1568.6 - 1569.7 19.1 - 29.3 5 Additional: carbon 1619.5 - 1621.7 9.6 - 16.6

CrystalSleuth did not show any reasonable match.

212

Figure 203. Raman spectra of garnet 8.

8.3 Discussion

We studied 8 different garnets, among which three belonged to the pyralspite group, four samples showed to be ugrandite and the last sample had a fingerprint with over-imposed organic matter and could therefore not be clearly identified. The 2nd and the 6th sample showed vibrations which were characteristic for both almandine nd -1 and spessartine. For example, the 2 sample had Eg at 914 cm , which is characteristic for -1 spessartine and a clear Eg at 368 cm , which is characteristic for almandine (Table 122, th -1 Figure 191). Another example is the 6 sample. It showed T2g+T1u at 499 cm , which is -1 characteristic for spessartine, while it showed a clear A1g at 347 cm , which is characteristic for almandine (Table 126, Figure 199). Assuming that the position of each Raman active mode results from linear combinations of the end-member wavenumbers weighted by their molar fraction, the approximate relation between the three end-members can be calculated. Using the method of Bersani et al. (2009), each peak was analysed and the ratio between pyralspite end-members was calculated. In this study, each peak was manually matched to a corresponding end-member with the help of the previously stated literature. Bersani et al. (2009) have created a special software for this purpose. The calculated results were plotted in a triangle plot, demonstrating the approximate relation between pyrope-almandine-spessartine (Figure 204). The 2nd and 6th sample showed ratios of 15:7 almandine-spessartine and 125:71 almandine-spessartine, respectively. The nearest almandine end-member showed to be the 7th sample.

213

Figure 204. Triangle plot, which illustrates the ratio of end-members in pyralspite group: 2nd, 6th and 7th samples. The 2nd sample also showed two additional peaks in the area 120 – 160 cm-1 (Figure 191). We believe that these two peaks are “marks” from the matrix and we assume that these two vibrations belong to quartz. The 2nd and the 6th samples did not show any characteristic vibrations for pyrope. The same ratio was calculated for the ugrandite group: 1st, 3rd, 4th and 5th sample. All four samples showed a very high content of grossular. The 4th sample was closest to the grossular end- member (Figure 205). The 3rd sample had the highest andradite content, up to 30%. It also -1 -1 showed mixed peaks, for example T2g+T1u at 995 cm and A1g at 877 cm were characteristic -1 -1 for andradite, while Eg at 368 cm and T2g+T1u at 275 cm were characteristic for grossular (Table 123, Figure 193).

214

Figure 205. Triangle plot, which illustrates the ratio of end-members in ugrandite group: 1st, 3rd, 4th, and 5thsamples The 1st and the 5th samples have one additional band at 1085 cm-1. We believe that this Raman vibration shows the presence of calcite in both samples (Table 121, Table 125). The 3rd sample has 5 additional bands: 150, 711, 1085, 1125 and 1320 cm-1. The first four additional bands are characteristic for calcite and the last mode is characteristic for carbon (Ferrari & Robertson, 2000). We believe that these additional peaks illustrate the calcitic chemistry of the 3rd sample’s host rock. The 1st, 3rd, 4th and 5th samples did not show any characteristic vibrations for uvarovite. The 8th sample showed only one peak, which was characteristic for almandine at 1035 cm-1. We believe that the rest of the peaks at 1262, 1385, 1568 and 1620 cm-1 (Table 128) show the presence of organic impurities (carbon), most probably on the surface of the sample (Ferrari & Robertson, 2000).

8.4 Conclusions Seven out of eight studied garnets have been identified. We did not observe any difference in the intensity of the two bands at 247 and 280 cm-1, which could have been markers for the grossular content, except for the nearly-pure grossular garnet. Using Bersani’s et al. (2009) approach, we could evaluate the ratio of different mixed end-members in the samples, as well as detect the signals of the host rocks, identify them and separate them from the garnets.

215

9 Final discussion and conclusions

The research presented in this work is both quantitative and qualitative. It covers a wide range of different minerals, including some rare ones, such as cerussite, ancylite, witherite and burbankite. In total, 25 different minerals, or 66 samples, were identified, characterised and discussed. With the help of Raman spectroscopy, one mineral was found to have been incorrectly identified in the collection - previously expected fluorite, by experiment showed to be calcite. While testing our hypothesis, the following main questions were asked: Is the agreement/disagreement between the published and acquired spectra sufficient to be conclusive about the deviations from an ideal chemistry? Is a specimen pure mineral or a mixture of minerals? The experiment showed that most results did not deviate much from the RRUFF references, except the additional or shifted peaks and occurence of a background, which pointed to the presence of impurities or to the fingerprint of the host rock. However, one mineral – burbankite - deviated substantially from the published spectra. Burbankite has a complex chemical composition, containing at least five different cations – Na, Ca, Sr, Ba and Ce. Two distinct, dissimilar Raman bands of the strong fluerescence were identified. We conclude that this mineral can exhibit a number of different Raman spectra due to its crystallographic complexity. Another important hypothesis that was tested during the analysis was the identification of the crystal structure defects, which were related to the stress-strain condition of the lattice, or the result of a natural heat treatment, as these variables reflect genesis of minerals, their geological history, for example subjection to metamorphic processes. We managed to identify such defects in the red corundum and in colourless quartz. The red corundum showed a broad (FWHM= approx. 60) additional peak at 258 cm-1, which likely represents traces of natural heat treatment, potentially caused by a regional metamorphism or even by a radiation source. The analysis of the shifted Raman bands of the colourless quartz showed that it retains tensile stress in the structure and was probably subjected to extending deformation. The residual stress is evaluated to be in the interval between 0.23 and 1.0 GPa. With the help of Raman spectroscopy, the polishing agent which is widely used in gemmology was identified and separated from the signals of studied minerals. While studying fluorite, we discovered that the intensity of the main peaks is directly dependent on the fluorite’s colour, i.e. on the host species, which are incorporated in the

216 crystal structure, such as metals, REE or even organic substances, and which give rise to the colouring of the mineral. Shifted peak positions usually serve as markers of deviations from an ideally pure and stress-free crystal. These imperfections also tend to enhance optical processes competing with the Raman scattering, most of all fluorescence. The fluorescence often results in the appearance of a broad background, which usually decreases the Raman signal-to-noise ratio. A broad fluorescence was identified in the almandine’s band, which can be potentially explained by the presence of REE in the garnet’s structure (Makreski & Jovanovski, 2008).

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