IR and UV-Vis Spectroscopy of Gem Emeralds, a Tool to Differentiate Natural, Synthetic And/Or Treated Stones?

FACULTEIT WETENSCHAPPEN Vakgroep Geologie en Bodemkunde

IR and UV-Vis spectroscopy of gem emeralds, a tool to differentiate natural, synthetic and/or treated stones?

Mathieu Van Meerbeeck

Academiejaar 2009–2010

Scriptie voorgelegd tot het behalen van de graad van Master in de Geologie

Promotor: Prof. Dr. K. De Corte Co-promotor: Prof. Dr. P. Van den haute Leescommissie: Prof. Dr. P. De Paepe, Prof. Dr. P. Vandenabeele

PREFACE AND ACKNOWLEDGEMENTS

I’d like to thank my promotor Prof. Dr. Katrien De Corte and HRD Antwerp for giving me the opportunity to perform this unique investigation. Her support, enthusiasm, patience and criticism during the progress of this research have really inspired me. I’m also thankful for the scientific, technical and gem-related assistance of her colleagues, Jef Van Royen and Anita Colders. Nathalie Crepin also gets some of the credit, by providing me with important articles.

It has also been nice working with the research staff in Lier, with special attention to the head of research, Mr. Yves Kerremans, and lab assistant Wendy Lembrechts, who initiated me with the instrumentation.

The recognised experience of professor Peter Van den Haute, my co-promotor, truly helped me create a fully scientifically based work. My appreciation goes to Prof. Dr. P. De Paepe and Prof. Dr. P. Vandenabeele as well, who put time and effort in the critical analysis of this thesis.

I also show my gratitude to my colleague student and friend Tim Verstraeten, who performed a similar study on sapphires. He was a great co-worker during data acquirement and our discussions lead me to several new insights.

Further, I’d like to thank everybody who improved this thesis with some necessary language corrections. And of course I should not forget my parents, who gave me the chance to study and who supported me during the progress of this thesis.

Cover picture: http://www.modernjeweler.com/web/online/colored-gemstone-gem-profiles/emerald/1$451.

ABSTRACT

As emerald is one of the most valuable precious stones, research on its characteristics and origins is of great importance in the gem industry. Until now, non-destructive methods to determine all provenances are however not sufficient. Therefore, we test the added value of two non-destructive spectroscopic methods to (1) distinguish synthetic from natural emeralds, (2) discriminate between the different provenances of the natural or the type of the synthetic emeralds, (3) determine the presence of filling substances (treatments). Spectroscopy in the visible and ultraviolet region (UV-VIS) and in the infrared (IR) region, using the Fourier Transform principle (FT-IR) were performed on a set of 133 cut emeralds.

By making classifications based on our own spectral observations, we were able to assign 78 % of the emeralds to the right origin. We separated all synthetic from natural emeralds and recognised all natural Colombian emeralds, synthetic flux and synthetic hydrothermal emeralds. Zambian emeralds have also been distinguished, with only 4 on 29 inconsistencies.

By applying UV-VIS spectroscopy, four major groups of emeralds could be distinguished: (1) flux synthetic emeralds, (2) Colombian and chlorine bearing hydrothermal synthetic emeralds, (3) copper bearing hydrothermal synthetic emeralds and (4) all other natural emeralds. Further IR spectroscopic analysis allowed a further determination in specific origins.

Treatments are recognised by absorptions in the IR region in the 3100-2800 cm-1 range. Unfortunately, further identification is not possible because of very similar absorption features by many types of filling substances an mixtures. TABLE OF CONTENTS

1. INTRODUCTION ...... 3

2. CHARACTERISTICS, GENESIS AND LOCALITIES OF EMERALDS...... 4

2. 1. SITUATION: HISTORY AND IMPORTANCE OF EMERALDS ...... 4

2. 2. CHARACTERISTICS OF EMERALD ...... 4 2.2.1. Crystal chemistry of beryl ...... 4 2.2.2. Colouration ...... 5 2.2.3. Channel ions ...... 6 2.2.4. Inclusions ...... 7

2. 3. TREATMENT OF EMERALDS ...... 8

2. 4. DEPOSITS OF EMERALDS...... 9 2.4.1. Origin conditions ...... 9 2.4.2. Important deposits ...... 11

2. 5. SYNTHETIC EMERALDS AND IMITATIONS ...... 15 2.5.1. Synthetic emeralds ...... 15 2.5.2. Imitations ...... 16

3. METHODOLOGY ...... 17

3. 1. RESEARCH STRATEGY AND PROGRESS ...... 17

3. 2. SPECTROSCOPY AS RESEARCH TECHNIQUE ...... 17 3.2.2. Infrared spectroscopy ...... 18 3.2.3. UV-VIS Spectroscopy ...... 23

4. RESULTS AND DISCUSSION ...... 26

4. 1. DESCRIPTION OF A TYPICAL EMERALD SPECTRUM ...... 26 4.1.1. The UV-VIS region ...... 27 4.1.2. The IR region ...... 29

4. 2. OBSERVATIONS AND INTERPRETATIONS ...... 31 4.2.1. Step 1: blind classification ...... 31 4.2.2. Step 2: classification based on reference samples ...... 37 4.2.3. Step 3: Comparison with the dataset of HRD Antwerp ...... 41

4. 3. SPECTROSCOPIC FEATURES OF NATURAL EMERALDS ...... 42 4.3.1. Colombia ...... 43

4.3.2. Brazil ...... 46 4.3.3. Zambia ...... 47 4.3.4. India ...... 49 4.3.5. Madagascar ...... 50 4.3.6. Sandawana (Zimbabwe) ...... 50 4.3.7. South-Africa ...... 52

4. 4. SPECTROSCOPIC FEATURES OF SYNTHETIC EMERALDS ...... 53 4.4.1. Natural versus synthetic flux versus synthetic hydrothermal emeralds ...... 53 4.4.2. Hydrothermal synthetic emeralds ...... 54 4.4.3. Flux-grown synthetic emeralds ...... 61 4.4.4. Additional features to distinguish synthetic from natural emeralds ...... 64

4. 5. THE QUESTION MARK GROUP OF THE STUDIED EMERALDS ...... 65

4. 6. TREATMENTS OF EMERALDS ...... 67 4.6.1. How to determine the presence of treatments in emeralds ...... 67 4.6.2. The information problem ...... 68

4. 7. DISCUSSION ...... 70 4.7.1. Internal differences in emerald origins ...... 70 4.7.2. The value of spectroscopy for emerald origin determination purposes ...... 71 4.7.3. Polarised or non-polarised spectra for emeralds? ...... 72

4. 8. FURTHER RESEARCH ...... 72

5. CONCLUSIONS ...... 74

6. REFERENCES ...... 75

7. APPENDICES ...... I

7. 1. LIST OF ALL ABBREVIATIONS AND SYMBOLS USED IN TABLES ...... II

7. 2. DETAILS OF UV-VIS AND IR FEATURES OF ALL KNOWN AND UNKNOWN ORIGINS ...... III

7. 3. DETAILS OF ALL SAMPLES: CHARACTERISTICS, CLASSIFICATIONS, TREATMENTS, DETAILS OF UV-VIS AND IR SPECTRUM ...... VII

8. ABSTRACT (DUTCH) ...... I

1. INTRODUCTION

Emerald, the green variety of beryl is one of the top precious stones used in jewellery. Gemmologists cope with three tasks when it comes to testing emeralds. They need to discriminate natural from synthetic or false, then they face a determination of the locality of the emerald and lastly, they have to identify a possible treatment. In order to fulfil these tasks, some quick, accurate and non-destructive techniques are desirable.

Until now, non-destructive research on emerald origin determination has mainly focused on microscopic analysis of internal structures and inclusions. Other techniques, like EDXRF (Stern and Hänni, 1982) and PIXE/PIGE (Yu et al., 2000, Calligaro et al., 2000), lead to some fruitful results reporting significant differences in element concentrations. However, all these technique still cannot infallibly fulfil the gemmologists tasks.

Spectroscopic techniques have been practiced as well. So far, large scale analyses have focused (1) on the explanation of the emerald spectrum (the work of Wood and Nassau, 1968 is still well recognised), (2) on differences in the infrared region between natural and synthetic (Stockton, 1987) and (3) on the identification of treatments, also in the infrared region (Johnson et al., 1999, Armstrong et al., 2000). Both in the ultraviolet- visible light and infrared region, some smaller scale studies on certain localities are performed. To our knowledge however, a large scale comparison of UV-VIS and IR spectra between different provenances or synthetic types is inexistent.

Our dataset contains 133 emeralds from different synthetic types and natural provenances. We perform two spectroscopic techniques: one in the ultraviolet-visible light region (UV-VIS) and Fourier-transform spectroscopy in the infrared (FT-IR) region. By applying these techniques, we test whether they are useful to (1) discriminate between natural and synthetic emeralds, (2) discover features typical for certain provenances or types of synthetics, and (3) identify possible treatments. The advantage of these methods lies in the quick measurements, high resolution and the relative low cost of the instrumentation. The weakness is that quantitative analysis on gems is not possible and therefore statistical examination on composition differences cannot be applied.

The first section of this work describes all useful information on the mineral emerald. The next chapter deals with a detailed explanation of the followed research strategy and gives background information about the spectroscopic techniques. Thereafter we present and discuss our results. In this chapter, we will also first explain the details known from literature, followed by our own observations and a comparison with literature. Finally, our conclusions will be highlighted.

2. CHARACTERISTICS, GENESIS AND LOCALITIES OF EMERALDS

2. 1. Situation: history and importance of emeralds

Emerald is derived from the Persian word ‘zumurrud’, and appears in Greek as 'smaragdos' meaning 'green stone', but it was only restricted to the green beryl variety since their discovery in Upper Egypt thousands of years ago (400 B.C., perhaps earlier, Jennings et al., 1993). Spaniards were responsible for the introduction of emerald in Europe and Asia, when they conquered South-America in the 16th century and ‘rediscovered’ the Colombian emerald mines (Sinkankas, 1981). Currently Colombia is still the largest producer and exporter, with an estimated 60 % of the world’s emerald trade (Behmenburg, 2002).

Emerald ranks with diamond, sapphire and ruby as being the most precious of stones. It’s quality – and price – is dominantly based on colour. For a good quality, cut emerald with strong blue-green colour, prices may reach easily to $ 2.500 per carat (= 0,2 g), but the real exceptional pieces may command more than $ 15.000 per carat. An example of the high value of emerald is demonstrated by a 10,11 carat Colombian emerald that was sold in 2002 for more than one million dollars (Behmenburg, 2002).

Another price determining factor is the provenance of the emerald: some are more sought-after than others. Consequently their market price will rise as if they are trademarks. This explains the rising interest in research on provenances the last decades.

To emphasise the colour and brilliance and fit them into jewels, emeralds are cut into various forms. This is usually a step cut, faceted or a cabochon.

Emerald typically contains surface reaching fissures and fractures that impact on their value. It is therefore a common practice in the emerald industry to enhance a gem’s appearance and subsequently its beauty, by filling these imperfections with foreign substances.

2. 2. Characteristics of emerald

2.2.1. Crystal chemistry of beryl

Beryl is a cyclosilicate, corresponding to the formula Be3Al2(Si6O18) (Figure 2.1) in which the SiO4 tetrahedra polymerise to form six-membered rings. These rings are stacked forming large channels parallel to the c-axis, that can be filled with alkalis or even water. Table 2.1 lists the main chemical and physical characteristics of emerald.

Table 2.1. Chemical, physical and optical characteristics of emerald (o = ordinary axis, e = extraordinary axis). After Sinkankas (1981).

Chemical formula Be3Al2(Si6O18) Cleavage Indistinct basal cleavage

Crystal system Hexagonal Fracture Conchoidal

Form Long and prismatic Refractive index (RI) 1.591 (o) and 1.584 (e)

Colour Deep green, blue-green, yellow-green Birefringence 0.007

Lustre Vitreous Optical sign –

Specific gravity (SG) 2,67 - 2,84 g/cm³ Pleochroism Weak to distinct: yellowish green – bluish green

Hardness 7,5 - 8 Fluorescence Inert to weak: red

Possible channel ions. After Sinkankas (1981).

H2O (2 types, depending on orientation)

Li, Na, K, Ce

In lesser proportions Ca, Mg

Other elements also possible

Figure 2.1. Beryl structure on a plane perpendicular to the c-axis, with in this case empty an empty channel. The accompanying table lists possible channel ions (Wood and Nassau, 1968). 2.2.2. Colouration

Pure beryl is probably inexistent in nature: substitution of Be and particularly Al by divalent or trivalent ions is always present in some degree. These substitutions are also responsible for the diversity of colours beryl can adopt. When (quasi) pure, beryl is colourless, but the substitution of certain trace elements for aluminium on the Y spot in the mineral structure causes various colours (Table 2.2). The valence state of the substitutes makes difference: for instance divalent Fe produces a bluish colour while the trivalent counterpart provides a yellowish

5 colour. To create the emerald deep green colour, a small amount of the transition metal chromium Cr3+ or, less commonly, V3+ has to substitute for Al3+ (Wood and Nassau, 1968). This is because these elements are chromophoric: due to the configuration of electrons around the atomic nucleus, chromium and vanadium selectively absorb purple, yellow and a part of the red light and transmit blue and green (and a little red). Some emeralds also contain a significant amount of divalent iron, which results in a more yellow-green colour. Neither heat nor irradiation affects the chromium- or vanadium-caused colours (although it may be possible to remove a trace of yellow if additional Fe is present) (Nassau, 1983).

When Wood and Nassau (1968) discovered that not only Cr, but V as well was a colouring agent of emerald, there was some discussion about the definition of emeralds: is it the presence of chromium that is the deciding factor, or the depth of colour as the criterion, whatever the colour-causing impurity. The definition that appears attaining most acceptance is the one of Schwarz and Schmetzer (2002):

“Emeralds are yellowish green, green or bluish green, natural or synthetic beryls, that reveal distinct Cr and/or V absorption bands in the red and blue-violet ranges of their absorption spectra.”

Table 2.2. Beryl varieties. After Sinkankas (1981).

Type Colour Assignment Type Colour Assignment

Goshenite Colourless Maxixe beryl Dark blue Defect in structure, by irradiation Emerald Deep green Cr3+, V3+ Bixbite Red Mn Green beryl (no Green V, Fe2+, Fe3+ Morganite Pink Mn emerald) Aquamarine Light blue Fe2+ Yellow/Golden Yellow, gold Fe3+ beryl / Heliodor

Fluorescence is not an important factor in emerald. Some species may glow weak red under ultraviolet light. Certainly when trivalent iron is present, fluorescence is quenched immediately (Nassau, 1983).

2.2.3. Channel ions

To maintain charge balance, substitutions may also be compensated by ions or molecules entering the channel sites of the beryl lattice. Hydroxyl ions may replace oxygen atom of the ring, or a water molecule may be entrapped in the ring channels. Water can do so in two ways, with the H-H bond parallel (type I) or perpendicular (type II) to the c-axis (Figure 2.2). Alkali ions are because of their small size also easily trapped in the channels. CO2 fits as well in the rings of the emerald structure (Wood and Nassau, 1968).

Figure 2.2. Channel entrapment of water and alkalis (Wood and Nassau, 1968). 2.2.4. Inclusions

Clean emeralds are very rare: almost all specimens show presence of inclusions that are trapped during or after crystal growth. Gemmologists are obviously interested in inclusions, because too many of them can make gem material worthless. But they are of interest for other reasons too: certain inclusions are distinctive and may even serve to identify the particular deposit from which they came. Inclusions also provide evidence as to the geochemical environment in which the beryl crystals grew (Table 2.3).

Table 2.3.Typical mineral inclusions in emerald. After Sinkankas (1981).

Type of emerald Inclusions

Austria: Habachtal, Apatite, biotite, chlorite, epidote, hematite, rutile, titanite, black tourmaline, tremolite Ural Brown mica, quartz, biotite, calcite, phlogopite, quartz, talc, tourmaline Colombia: Chivor, Gachala Albite, halite, pyrite (only Chivor), quartz (only Chivor) Colombia: Muzo Albite, calcite, carbon (trapiche), halite, parisite South-Africa: Transvaal Biotite, calcite, molybdenite, pyrite Brazil: Goiaz Biotite, dolomite, rutile, talc Brazil: Salininha, Bahia Calcite, feldspar, phlogopite, talc Zimbabwe: Sandawana, Feldspar, garnet, hematite, tremolite India: south Chlorapatite India: north Fuchsite Synthetics Chromite, pyrrhotite, pentlandite

2. 3. Treatment of emeralds

Despite its hardness, emerald is very brittle and can be easily fractured. To disguise the frequent appearance of flaws and thus enhance the lustre, the minerals are impregnated with organic or synthetic compounds with comparable specific gravity (SG) and refractive index (RI), a tradition that has been practiced since antiquity. Like an ice cube that loses its relief when put in clear water, a fissure in emerald becomes less visible when it is filled with a substance that has close RI to that of emerald. Johnson et al. (1999) divided the filling substances into six categories1 (Table 2.4). The most used (presumed2) natural filling is cedarwood oil. The main artificial3 filling is Opticon 224. The durability (colour switch, volatility) of the fillings is variable and some need to be renewed after a few years. However, even after more than 20 years traces remain, large enough to allow identification (Nassau, 1984, Armstrong et al., 2000).

Table 2.4. Classification of emerald filling substances. After Johnson et al. (1999).

Category Natural / Properties Main examples artificial

Essential oils (including Presumed Extracted from host plants using solvents. They Cedarwood oil, Canada balsam natural resins) natural are volatile, so not very stable over long time.

Other oils Presumed Mineral, vegetable oils Paraffin oil natural

Waxes Presumed Beeswax, spermaceti, vegetable wax, mineral Paraffin wax natural wax

Epoxy prepolymers; Artificial resin For emerald filling purposes, most (pre- Opticon 224, Epon 828, Araldite other prepolymers; )polymers contain one type of an epoxy 6010, Palm oil (“Palma”), polymers molecule: DGEBA. Polymers are hardened PermaSafe, Gematrat prepolymers.

Sometimes a green colour is added to the filling. This “dying”, particularly associated with Opticon, enhances the gem colour and may therefore be considered as a form of deception. Moreover, in some markets emeralds that underwent certain treatments, like Opticon, are less desired than other treatments such as cedarwood oil. The major coloured stone trade organisations recommend that treatments should be disclosed at every stage of the distribution process, but the debate on what and how it should be disclosed still goes on (Johnson et al., 1999).

1 This classification tries to rule out all ambiguity both in meaning or in terms applied by different branches of chemistry 2 Chemical synthesised equivalents are not distinguishable. 3 Without a natural equivalent. 8

In our thesis we will take into account the influence of these fillers on the IR and UV-VIS spectra. Several spectral analysis studies in the MIR region have already proved the success to detect fillers (e.g. Beesley, 2006, Armstrong et al., 2000, Johnson et al., 1999). However, an unambiguous identification of a certain treatment based only upon spectroscopy is very difficult, because of the sometimes minor spectroscopic differences and the possible use of mixtures.

2. 4. Deposits of emeralds

2.4.1. Origin conditions

The rarity of beryl is due to the fact that there is very little Be (2,1 ppm) in the upper continental crust, unlike Cr and V. These elements are more common (92 and 97 ppm respectively) and concentrated in dunites, peridotites and basalts and their metamorphic equivalents (Rudnick and Gao, 2003). Consequently, special geologic conditions are required for Be to meet Cr and/or V.

The ‘classic model’ (as called by Walton, 2004, Groat et al., 2008) states that emerald formation occurs in the metasomatic contact zone between Be-bearing pegmatites and the Cr- and/or V-bearing host rock. This host- rock is typically a metamorphosed serpentinised peridotite, amphibolite, greenstone or another mafic or ultramafic rock. Contact boundaries can be tectonic or intrusive and the resulting contact zones are generally biotite or phlogopite shists. Figure 2.3 depicts a schematic representation for this pegmatite/schist-hosted model.

Another model explains the presence of emerald in the Colombian black shale deposits, that are unusual because there is no evidence of magmatic activity. According to Ottoway et al. (1994), hydrothermal highly alkaline circulation fluids from evaportic origin migrated upwards where they interacted with the organic-rich black shales to form emerald. The hydrothermal brines transported evaporitic sulphate to structurally favourable sites, where it was thermochemically reduced. The resulting sulphur reacted then with organic matter in the shales to release trapped Cr, V and Be, which enabled emerald formation.

Figure 2.3. Schematic overview of a typical emerald deposit (Walton, 2004).

It became obvious that regional metamorphism and tectonometamorphic processes such as shear zone formation plays a significant role in certain emerald deposits (Kazmi, 1989). After all, the majority of the deposits is situated in or near to suture zones. The classical model wasn’t that simple as it seemed: emeralds can form in a wider variety of geological environments than previously thought. Some emerald deposits show evidence of brine fluid involvement of metamorphic origin and don’t necessarily contain pegmatites, like for example in Pakistan (Kazmi, 1989), South-Africa (Grundmann and Morteani, 1989) or Austria (Grundmann and Morteani, 1989).

2.4.2. Important deposits

While emeralds have been found in over hundred locations on each continent (except for Antarctica) throughout the world (Figure 2.4), most are not commercially viable or do not produce gemstone quality material. Below is a record of the relevant mining sites that produce emeralds of fine quality and/or in large volumes. In Table 2.5 we list some of their geological and chemical features that might be interesting for our investigation.

Figure 2.4. Important (big dots) and smaller emerald deposits in the world. After a compilation of references, mentioned in text.

a) Brazil

The states of Minas Gerais, Bahia and Goiàs produce the most significant quantity of emeralds and other gemstones of Brazil. They are all found in biotite shists. Giuliani et al. (1997) divided the Brazilian emerald deposits into two classes: (a) those associated with pegmatites (Minas Gerais, Bahia) and (b) those related to metamorphic fluids and ductile shear zones (Goiàs). Both are estimated to have formed around two billion years ago. Brazilian emeralds are rather pale, in some cases taking on a yellowish hue.

b) Colombia

Colombia produces the highest quality and quantity emeralds in the world. Their bluish green colour is so perfect that almost no other country can compare. Ottoway (1991) suggested that the removal of Fe from the system as pyrite is an important factor of this intense colour, because Fe3+ quenches the red fluorescence (§ 2.2.2, p. 5). Colombian deposit are the only large deposits related to black shales and mineralisation occurred at ~ 35 Ma. Muzo, Chivor and Cosquez and since recently La Pita, are the most important deposits, but there are over 200 occurrences (Groat et al., 2008). A special kind of emeralds, only found in Colombia, are the trapiches (Figure 2.5), in which inclusions form a six-rayed pattern coinciding with this hexagonal prism. Nassau and Jackson (1970) attributed this phenomenon to dendritic growth in which the corners grow faster than the faces (not asterism). The inclusions consist mainly of albite.

Figure 2.5. Cut trapiche emerald (http://www.jewelryexpert.com).

a) India

The discovery of emerald in India occurred only in the 1940s in the northwest (Rajasthan state). Emerald bearing veins occur at the contact between pegmatites and talc, biotite and actinolite schist. In the southern state Tamil Nadu, emerald was found only in the mid 1990s, and gemmological research revealed significant similarities in physical properties, inclusions and compositions with Madagascar emeralds, suggesting that they probably deposited before the rifting of the Indian plate, 200 Ma (Panjikar et al., 1997).

b) Madagascar

Deposits contain Cr-rich emeralds and are found in two major areas, both formed approximately at 500 Ma: in the Mananjary region, pegmatites are hosted by phlogopite-rich rocks formed through metasomatism of Cr-rich meta-ultrabasites (Moine et al., 2004). Emeralds from the Ianapera deposit may have formed from circulating metamorphic fluids resulting form granulitisation and devolatilisation of the lower crust due to shearing (Andrianjakavah et al., 2009). This last deposits contain the highest reported concentrations of alkali’s and chromium oxides (Vapnik et al., 2005).

c) South-Africa

World’s oldest emeralds formed at 2,97 Ga, during a period of regional metamorphism and occur in the contact zone between a metasomatised pegmatite body and mafic schists. Excavation began in 1980 in northern Transvaal (Grundmann and Morteani, 1989).

d) Zambia

Zambia is also one of the most important sources of emeralds, where mines are located in the Kafubu area, excavated since 1928. Emeralds originated when pegmatite veins intruded metamorphosed komatiites, approximately 450 Ma ago (Zwaan et al., 2005).

e) Sandawana (Zimbabwe)

Mines are mainly located in the Sandawana area, and were only discovered in 1956. Sandawana emeralds have become well known for their splendid colour and the typical small size. They probably formed during deformation at 2,6 Ga, when pegmatites intruded the greenstones. Emeralds contain a very high Cr and alkali content (Zwaan et al., 1997).

f) Other deposits

Other interesting deposits throughout the world are located in Afghanistan, Australia, Austria, Bulgaria, Canada, China, Egypt, Mozambique, Namibia, Nigeria, Norway, Pakistan, Russia (Ural), Somalia, Spain, Tanzania, Ukraine, USA.

Table 2.5.Geological and chemical features of emeralds from the discussed deposits. Compilation of references.

Deposit Brazil Colombia Southern India Madagascar Zambia Zimbabwe

Features

Type of Pegmatite veins Black shale Pegmatites Pegmatites; Pegmatite veins Pegmatite veins deposit intruding biotite with brine intruding talc shear related intruding intruding schists; shear circulation schist circulation metabasites greenstones related fluids

Mineral age 1,9 Ga 30-35 Ma >200 Ma 500 Ma 450 Ma 2,6 Ga

Colour of Light green, Deep bluish Pale to medium Pale to medium Bluish green Vivid green with emeralds yellowish green green, deep green green with a medium medium to dark green to dark tone tones

Cr content Low Very high High Very High Mod. Very High

V3+ High Very low Low Low to high Low Very low

Iron Fe2+ and Fe3+, Very low Unknown Fe2+ (high )and Fe2+ and Fe3+ Fe2+ (mod.) content high Fe3+ (mod.) (mod. to high)

Alkali Mod. Low to mod. Unknown High Mod. High content

Add. High Cu Similarities with High Cs & Li High Cs information Madagscar

Reference (Preinfalk et al., (Banks et al., (Groat et al., (Andrianjakava (Zwaan et al., (Zwaan et al., 2002, Zwaan et 2000, 2008, Panjikar h et al., 2009, 2005) 1997) al., 2005) Ottaway, et al., 1997) Vapnik et al., 1991) 2005)

2. 5. Synthetic emeralds and imitations

2.5.1. Synthetic emeralds

Because of emerald’s enormous commercial value, a remarkable number of synthetic emeralds have entered the market over the past five decades. Two important growth techniques are present to synthesise emerald. The first one is the flux-fusion process, a method invented in and perfected since the late 1930’s (O'Donoghue,

1997). A flux is a substance that reduces the melting point of certain materials. Examples are LiO, MoO or PbF2. Substances like beryllium -, chromium - and aluminium oxide, that normally have very high melting points, are mixed with the flux substance in a crucible, their melting temperature lowers to a point where they become supersaturated and crystallisation occurs, with or without the use of seed crystals. This way the flux speeds up crystallisation at lower (atmospheric) pressure and temperature (in the region of 1000 °C). This process does not include water. Table 2.6 lists the different flux-fusion techniques commonly used for emerald synthesis.

Another method is the hydrothermal growth process, that originated in the 1960’s by Lechleitner (Schmetzer et al., 1997, Adamo et al., 2005). The principle is to increase the solubility using solutions at high P and T: this is analogous to gem growth in pegmatites and the resulting minerals are therefore much harder to identify as synthetics than flux grown emeralds. This process is imitated in an autoclave filled with water, feeding material and one or a few seed crystals (a synthetic or low quality emerald). High temperatures and pressures (in the order of 600°C and 2kbar respectively) around the feeding material cause it to dissolute, migrate and precipitate around the cooler seeds. Several hydrothermal techniques can be found in Table 2.6.

Table 2.6. Flux & hydrothermal emerald synthesis techniques with their chromophore(s) (O'Donoghue, 1997, Schmetzer et al., 1997, Adamo et al., 2005).

Flux Hydrothermal Hydrothermal

Chatham – Cr Lechleitner (Austria) – Cr + Cu Russian – Cr + Cu

Gilson – Cr Linde – Regency (same method, Tairus (Russ. + Thailand) – V + Cu USA) – Cr

Lennix – Cr (USA) – Cr Chinese – Cr

Taiwan – Cr Biron (Australia) – Cr + V Malossi (Czech) – Cr

Russian – Cr Pool – Cr + V AGEE (Japan) – Cr + V

Synthetic emeralds can be distinguished upon several features. Unusual inclusion forms or contents, a lower SG or RI or strange growth structures are normally sufficient to recognise them. In this thesis we will discuss how UV-VIS and IR spectroscopy can identify these different types.

2.5.2. Imitations

Although they are mostly honestly presented as being not real, caution is always required for this type of adulteration. Many green materials exist and may be falsely sold as emerald, even though traditional gemmological techniques are sufficient to discriminate between them (Chelsea filter4, SG, RI and/or a microscope should do the job already). Table 2.7 contains the most important imitations and their selling names. Another type are the doublets or triplets: two or three green or pale coloured stones glued together with a (green) paste, creating a stone resembling emerald.

Table 2.7. Emerald imitations.

Imitation Market name Imitation Market name

Chrome diopside Peridot Evening emerald/Night emerald

Demantoid garnet Uralian emerald Prehnite Cape emerald

Dioptase Congo emerald Green Quartz (treated) Indian / Gibsonville emerald

Fluorite (South-)African, Bohemian, Chalcedony dyed green Emeraldine Traansvaal emerald

Green glass Green sapphire Oriental emerald

Hiddenite (green Lithia emerald Spinel Spodumene-variety) Green tourmaline Verdelite, Brazilian emerald

4 Not only green, but also a part of the red light still passes when sent through emerald. Based upon this information, a clever optical filtering device was designed to help distinguish emeralds from imitations: the Chelsea filter. This filter absorbs green but passes red, and thus makes an emerald look (dull or bright) red when viewed through, whereas many imitations appear some dull colour. Synthetic emeralds are however harder to distinguish, since they also transmit (mostly much brighter) red light. 16

3. METHODOLOGY

3. 1. Research strategy and progress

A set of 133 cut emeralds from the collection of HRD Antwerp was available for study. The objectives are to discriminate – based only upon our own spectroscopic data – between (1) natural and synthetic, (2) the different geographic origins of natural emeralds or types of synthetics and (3) identify possible treatments. In order to work on this matter on a scientific basis, our approach is to achieve our goals in different phases:

- The first step is to discriminate in different groups without having any indication of type (synthetic, natural, type of treatment) or provenance. This is on the one hand a training to get in touch with the subject, but will also give us a direct idea of difficulties we will have to encounter.

- In a next step, we receive one or two samples matching different provenances or types. This way we can observe the significant differences, while we can keep in mind the difficulties encountered in step 1.

- The next step includes the comparison with the dataset and an evaluation of our classification. After this, we discuss the value of the two spectroscopic techniques for our purposes.

3. 2. Spectroscopy as research technique

Spectroscopy may be defined as the study of the interaction of electromagnetic waves and matter, and has many applications on all kinds of study areas. The non-destructive character of research on gems however limits this assortment to only a few forms. We focus hereby on ultraviolet-visible (UV-VIS) light and infrared (IR) spectrometry. The former deals with the measurement of absorption, reflection and emission of light in the near-ultra-violet, visible and a part of the near-infrared portion of the spectrum. IR spectroscopy exploits the vibrational properties of radiation (Following recapitulation is based on the works of Banwell and McCash, 1994, Hawthorne et al., 1988, Hollas, 1987, Pavia et al., 2009, Willard et al., 1965, Perkampus, 1995).

a) The electromagnetic spectrum

The electromagnetic spectrum is divided in several regions. Each region is associated with different modes of energy transitions, although the precise boundaries are chosen rather arbitrary (Table 3.1). Energies are very large at high frequencies, even so that they can ionise atoms or break bonds in molecules. At the other end, low energies are only enough to cause nuclear or electronic spin transitions within molecules.

Table 3.1. Types of energy transitions in each region of the electromagnetic spectrum. We focus on the regions coloured in grey.

Region of spectrum Wavelength range (m) Phenomena causing absorption Gamma rays 1 pm – 100 pm Rearrangement of nuclear particles X-Rays 100 pm – 10 nm Inner electron transitions Far-Ultraviolet 10 nm – 200 nm Loss of valency electrons Near-Ultraviolet 200 nm – 380 nm Valency electron transitions Visible 380 nm – 750 nm Valency electron transitions Infrared 0,75 µm – 300 µm Molecular vibrations Microwave 0,3 mm – 1 m Molecular rotations Radiofrequencies < 1 m Reversal of spin of nucleus or electrons

In spectroscopy wavelengths are expressed in a variety of units. It is usually given in micrometers (µm) – formerly called microns – or nanometers (nm). Another way to characterise electromagnetic radiation is in terms of wavenumber (WN). This is the number of complete waves or cycles contained in each centimeter length of radiation:

WN = 1/ λ (cm-1)

The main reason chemists prefer to use wavenumbers as units is that they are directly proportional to energy, while the numbers are still easy to work with.

b) Lambert-Beer law

This law states that there is a dependence between the absorbance (or transmittance), A (T), of light through a substance and the product of the molar absorptivity of the substance ε, the concentration of the absorbing element c and the distance the light travels through the material (i.e. the path length), ℓ:

where I0 and I are the intensity of the incident light and the transmitted light, respectively.

3.2.2. Infrared spectroscopy

Spectrometry in this region of the electromagnetic spectrum takes advantage of the vibrational properties of infrared radiation, which are enlightened first before a description of the instrument.

a) Infrared characteristics

The infrared region lies at wavelengths longer than those associated with visible light and ranges from 0,750 to about 300 µm, i.e. 13500 to around 30 cm-1. We divide it as follows:

 Near IR (NIR): 0,75 to 2,5 µm / 13500 to 4000 cm-1;  Mid IR (MIR): 2,5 to 50 µm / 4000 to 200 cm-1;  Far IR: (FIR): 50 to 300 µm / 200 to 30 cm-1.

Again, the classification of these sub-regions is merely conventional and in literature, boundaries may vary somewhat. But generally, each region has its features: FIR has low energy and studies explore rotational energy transitions while MIR and NIR constrain the vibrational portion of the infrared region. IR spectroscopy can be applied in the spectral region of about 800 to 50 µm or 13500 to 200 cm-1. We constrain our equipment to a region of 7000 to 400 cm-1 in which most normal vibrations of molecules are found.

b) Infrared absorption

IR spectroscopy exploits the fact that almost any compound having covalent bonds, absorbs various frequencies of electromagnetic radiation in the infrared region. In fact, the infrared spectrum is one of the most characteristic properties of a compound. It provides a fingerprint for identification and a powerful tool for the study of molecular structure. Empirical correlations of vibrating groups with specific, observed absorption bands offer the possibility of chemical identification. Moreover, when coupled with intensity measurements it can lead to quantitative determinations, but this is not applicable to our study.

The process: molecules are excited to a higher energy state when they absorb infrared radiation in a quantised way: a molecule absorbs only selected frequencies of infrared radiation. This happens when following two requirements are met: (a) if the natural frequency of vibrations of the molecule is the same as the frequency of the radiation and, (b) if the molecular bonds have a dipole moment. Therefore symmetric bonds (e.g. O2) do not absorb infrared radiation. Since every type of bond has a different natural frequency of vibration, and since two of the same type of bond in two different compounds are in two slightly different environments, no two molecules of different structure have exactly the same infrared absorption pattern. Thus, the infrared spectrum can be used for molecules much as a fingerprint can be used for humans.

An important note to be considered is that molecules may vibrate in different modes and this leads to the occurrence of different bands in the spectrum. Bonds can stretch and/or bend in many ways, like in Figure 3.1.

Figure 3.1. Stretching (left) and bending (right) (Pavia et al., 2009).

c) FT-IR Instrumentation and acquisition

We used the Thermo Nicolet NEXUS ™ 470 Fourier transform infrared (FT-IR) spectrometer from HRD Antwerp with a diffuse reflectance accessory. A photograph and a schematic presentation of this computer-interfaced FT- IR spectrometer are shown in Figure 3.2.

Figure 3.2. FT-IR: (a) Photo of the Thermo Scientific NEXUS ™ 470 FT-IR system (https://www.thermo.com) and (b) scheme showing the interferometer principle (Pavia et al., 2009).

Interferometer

This spectrometer uses a Michelson interferometer to process the energy sent to the sample. In the interferometer, the source energy passes through a beam splitter: a semi-translucent mirror placed at a 45° angle to the incoming radiation, which allows the incoming radiation to separate it into two perpendicular beams: one undeflected, the other oriented at a 90° angle. One beam, the one oriented at 90°, goes to a stationary or fixed mirror and is returned to the beam splitter. The undeflected beam goes to a moving mirror and is also returned to the beam splitter. The motion of the mirror causes the path length of the second beam to vary. When the two beams meet at the beam splitter, they recombine, but the path length differences of the two beams cause both constructive and destructive interferences. The combined beam containing these interference patterns is called the interferogram. This interferogram contains all of the radiative energy coming from the source and has a wide range of wavelengths.

The interferogram then passes through the sample, being here the gemstone lying on a table. The sample simultaneously absorbs its characteristic wavelengths that are normally found in its infrared spectrum. The modified interferogram signal contains information about the amount of energy that was absorbed at every wavelength and reaches the detector.

Fourier-Transformation

The information is contained in a time-domain signal that gets converted by a Fourier transformation to what we recognise as a typical infrared spectrum.

By a Fourier analysis, we understand the mathematical fact that any periodic or non-periodic function, y = f(x) can be written as a sum or an integral of sine and cosine functions of the argument. The interferogram is initially a complex plot of intensity versus time (a time-domain spectrum). However, the investigator is interested in a spectrum that is a plot of intensity versus frequency (a frequency-domain spectrum). The Fourier transform decomposes the time-domain representation into oscillatory functions so it can separate the individual absorption frequencies from the interferogram. This way it produces a spectrum virtually identical to that obtained with a normal dispersive spectrometer.

The computer then subtracts the background spectrum (which is previously obtained the same way as described above but with the absence of a sample) from this modified interferogram. The final interferogram is a plot that is essentially identical to that obtained from a traditional double-beam dispersive instrument.

The advantage of the FT-IR technique is that it acquires the interferogram in a very short time period (a few seconds). It is possible to collect a series of interferograms of the sample and accumulate them in the memory 21 of a computer. A Fourier transformation performed on the sum of the accumulated interferograms, results in a spectrum with a better signal-to-noise ratio.

Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) accessory

An interesting note is the build-in DRIFTS feature. Light that passes through a cut gemstone is scattered in a lot of directions due to the numerous facets. This accessory ensures that the infrared light is focused onto the gemstone and the scattered light is collected and relayed to the IR detector using a spherical mirror (Figure 3.3). This is an extra asset, since emeralds contain a lot of flaws and inclusions, hindering the passing light.

Figure 3.3. DRIFTS principle.

Other significant notes

It is important to update the background signal regularly (we refreshed each hour), because the amount of infrared-active atmospheric gases, carbon dioxide and water vapour (oxygen and nitrogen are not infrared active) might change significantly while exposed by air (i.e. during switching samples) and consequently influence the final spectrum.

Because of the double refraction of emeralds, the orientation of the gem on the table is of importance to measure intensities and thus concentrations. According to Beer’s law, we would also need the travelling distance of the light through emerald, a parameter which is very hard to obtain. Therefore, we decided not to include quantitive analysis as a goal of this thesis. Subsequently orientations on the sample table can be chosen randomly.

Samples need to be cleaned before measurement. Organic material that sticks on the outside of gems could be hindering the spectrum.

d) Software and presentation of the spectra

The OMNIC ™ (version 5.12) software supports acquisition and post-processing of the FT-IR spectra. The range is restricted between 7000 and 500 cm-1. To gain high resolution spectra, we perform 256 scans for each sample. By stacking this amount of scans, we can achieve the premised resolution of 1 cm-1 we assume to be necessary for our purposes. The disadvantage is that such a high resolution demands a spectrum measurement of approximately 10 minutes for each sample.

The absorption spectra are displayed in terms of absorbance in function of decreasing wavenumber i.e. increasing wavelength.

3.2.3. UV-VIS Spectroscopy

a) The absorption process

Absorption in the UV-VIS spectral region is like other absorption processes the result of the excitation of electrons from a state of low energy (the ground state) into to a state of higher energy (the excited state) and is also a quantised process: as a molecule absorbs energy, an electron is promoted from an occupied orbital to an unoccupied orbital of greater potential energy. The spectroscopic technique to measure the absorption is the same for UV as for visible light.

Table 3.2. Relation between absorption of light and colour.

Wavelength region (nm) Transmitted colour Complementary hue < 380 Ultraviolet 380 – 435 Violet Yellowish green 435 - 480 Blue Yellow 480 - 490 Greenish blue Orange 490 – 500 Bluish green Red 500 – 560 Green Purple 560 – 580 Yellowish green Violet 580 – 595 Yellow Blue 595 – 650 Orange Greenish blue 650 – 780 Red Bluish green > 780 Near infrared

b) Colour

Absorption in the visible ranges of the electromagnetic spectrum directly affects the colour of the material. When we observe light emitted from a source, as from a lamp, we observe the colour corresponding to the wavelength of the light being emitted. However, when white light falls on an object, particular wavelengths (dependent on the type of material) of the light beam are absorbed and the remaining light is reflected: our eyes perceive the colour that is complementary to the colour corresponding to the absorbed wavelengths (Table 3.2).

c) UV-VIS Instrumentation and acquisition

The InSpectrum CCD Array UV-VIS Spectrophotometer of HRD Antwerp has a typical arrangement of a light source, a monochromator and a detector. Since the wavelength range requires two different light sources to cover it, the spectrum is acquired in two steps: first with a deuterium lamp for the UV portion (250 to 725 nm), then the tungsten lamp spanning the higher wavelengths (625 to 1100 nm: this includes a part of the NIR). The monochromator is a diffraction grating; its role is to spread the beam of light into its component wavelengths. A system of slits focuses the desired wavelength on the sample table (Figure 3.4). The light that passes through the sample reaches the detector, which records the intensity of the transmitted light. The detector is here a series of photodiodes positioned side by side (CCD). Each diode is designed to record a narrow band of the spectrum. The diodes are connected so that the entire spectrum is recorded at once.

Figure 3.4. Detail of the UV-VIS instrument set-up. Photo: Mathieu Van Meerbeeck.

Because this is a single-beam mechanism, a preliminary background measurement is required (no sample in the pathway) to take surrounding light into account, even though measures take place in a dark environment. Division of the sample spectrum by that of the background leads to the final spectrum. We acquire a resolution of 1 nm.

d) Software and presentation of the spectra

The spectrophotometer is interfaced with the acquisition and post-processing software SpectraSense™, version 4.1.9. The UV-VIS spectrum record plots transmittance (unlike the IR measurements) versus wavelength. The spectrum ranges between at 250 nm and 1100 nm.

4. RESULTS AND DISCUSSION

In this chapter results are presented with respect to the different stages explained in the research strategy. We start with a general description of a typical emerald spectrum as reported in literature. As mentioned, FT-IR spectra are generally presented as wavenumber (cm-1) versus absorption, UV-VIS spectra in wavelength (nm) versus transmittance. Sample names start with “GE” followed by a series of numbers (and end mostly with “G”).

4. 1. Description of a typical emerald spectrum

The assignment of most of the peaks and bands is already described in literature and will be discussed here in order to optimise our classifications.

The research of Wood and Nassau (1968) on the spectroscopic characteristics of beryl is still a valuable work. Figure 4.1 depicts the composite spectrum of a typical beryl (yet representative for emerald) illustrating the most important bands in various spectroscopic regions.

Figure 4.1. Composite spectrum of beryl between 300 and 7500 nm showing the region of lattice vibrations, molecular vibrations, and chromophoric absorptions (Wood and Nassau, 1968). We investigated the 250 – 1100 nm (UV-VIS) and 7000 – 400 cm-1 (IR) regions.

Absorptions in the UV, visible and a part of the NIR region are caused by chromophoric transition metals, as mentioned in § 2.2.2, p. 5. Absorptions in the NIR-MIR between around 12000 and 6000 cm-1 originate from

-1 impurity molecules trapped in the beryl channels, dominated by H2O and CO2. From 2000 cm further into the infrared, mainly lattice vibrations of the beryl structure account for the spectrum.

4.1.1. The UV-VIS region

An example of a recorded non-polarised transmittance spectrum is depicted in Figure 4.2. The accompanying Table 4.1 lists the chromophores that give rise to absorption bands (broad), peaks (sharp) and shoulders (small kinks) (based on Wood and Nassau, 1968, Schmetzer et al., 1974). The orientation of the emerald during the spectrum acquirement matters, since emerald is double refractive. This way, peaks or bands may vary in size or position, or they may even not appear at all. But because of the limited extra value we expect it to give, the influence of the orientation is not an issue of this thesis. We are not aware of the possible presence of artefacts due to air contamination.

Figure 4.2. Example of a non-polarised UV-VIS spectrum of a natural emerald with assignments of the absorptions (GE03396G).

Table 4.1. Important absorptions and their assigned chromophores (Wood and Nassau, 1968). The maxima may vary little.

Wavelength Absorption type Associated Chromophore top (nm) colour 370 peak / band UV Fe3+ 430 band Violet Cr3+, V3+ 477 shoulder Blue Cr3+ 610 band Gr-Ye-Or-Re Cr3+, V3+ 636 peak / shoulder Red Cr3+ 660 shoulder Red Cr3+ 681, 684 (double) peak Red Cr3+ 830 band NIR Fe2+

957 peak NIR H2O * * No chromophore

Cr3+ gives rise to the two broad bands at approximately 430 and 610 nm, seen in all emerald spectra (after all, these bands formulate the definition of an emerald, see § 2.2.2, p. 5). This produces the green colour, accentuated by the low absorption in the green and the steep slopes of the absorption bands. However, the exact top and slopes may differ significantly due to sample orientation or differences in composition, resulting in different shades of green. Chromium is also responsible for some smaller peaks that may appear; most clear is the absorption doublet at 681-684 nm. Absorption bands of V3+ are very close to those of Cr3+ in emerald (Figure 4.3): in Cr-poor emeralds, the two broad bands around 430 and 610 nm are also found, but the frequencies and relative intensities are quite different for the two kinds of crystal. V3+ does not cause the smaller peaks, nor the doublet at 681-684 nm, although vanadium that is not in the trivalent state may cause a small shoulder at 680 nm.

Figure 4.3. Polarised spectra of (a) a Cr-free emerald and (b) a Cr-rich emerald (Wood and Nassau, 1968). Dashed lines = extra-ordinary ray, full lines = ordinary ray.

Iron may be present in divalent or trivalent form. Fe2+ causes a broad absorption band with a maximum (i.e. minimum on our transmission graphics) between 800 – 850 nm. Emeralds containing Fe3+ show a peak around 370 nm.

A last important peak is the one at 958 nm. We are not aware of literature that accounts for this peak in emerald but we are however confident that it is caused by water, because: (1) we are in the molecular vibrational region that is dominated by water and CO2, (2) Wood and Nassau (1968) bring up that the peak is present in other types of beryl, and (3) one reference assigns it to water in morganite (Laurs et al., 2003).

Further, Cu2+ replacing Be2+ may form a band at 750 nm, but this feature has only been significantly found in hydrothermal synthetic emeralds (Schmetzer, 1988).

4.1.2. The IR region

Absorptions in the IR are presented in Figure 4.4 and Table 4.2. Wood et al. (1968) discovered already that all natural emeralds have strong absorption bands in two regions: the 3200 to 4000 cm-1 band and the area from around 2200 cm-1 farther into the infrared. The former is caused by trapped water (type I and II), the latter by other atoms or groups of atoms in the beryl crystal structure, e.g. SiO4 bands. A detailed view of these regions is unfortunately only possible when using fine samples and thus destructive methods. This forces us to focus our analysis on other regions. We therefore also might cut the part between 2000 and 400 cm-1 away on subsequent presented spectra.

Figure 4.4. Example of an emerald FT-IR spectrum between 7000 and 400 cm-1 (GE03385).

Table 4.2. Some emerald absorptions in the IR (Wood and Nassau, 1968).

Wavenumber top (cm-1) Type Assignment (approx.)

6850 shoulder H2O 5450 shoulder H2O type I 5273 peak H2O type II 5100 shoulder H2O type I 4000-3200 band H2O TI and II 2357 peak CO2 2200-400 band lattice vibrations

The first absorption peak around 6850 cm-1 is actually a shoulder of a large TII water absorption peak at 7068 cm-1, not seen in our spectra. Another strong absorption due to this type of water is a peak around 5275 cm-1 surrounded by two rounded shoulders. The middle sharp peak is due to type II water, while the shoulders are both assigned to type I. These shoulders are very expressed in low-alkali emeralds, and are accompanied by a fine middle peak. When a high alkali content is present, there is more like one large triangular shaped absorption peak. In low-alkali emeralds, the orientation of the sample may influence the intensity of the peaks and shoulders, because of the perpendicular orientations of these elements in the beryl structure (Figure 4.5).

Figure 4.5. Details of non-polarised infrared spectra of a Chinese hydrothermal synthetic emerald. Direction (A) perpendicular to the c-axis, (B) slightly oblique to the c-axis. They illustrate how the three main peaks at 5400, 5273 and 5100 cm-1 can vary in intensity depending of orientation of the sample (after Schmetzer et al., 1997).

Fortunately, between the two broad bands is a low absorption window between 3200 – 2200 cm-1: this is an interesting region because trapped CO2 and C-H (interesting to determine organic oil treatments) stretching -1 bands occur here. The CO2 gives rise to the sharp peak at 2357 cm , smaller shoulders surrounding it and a peak at 2291-93 cm-1.

FT-IR spectroscopy has already proved its value for fracture filling detection (e.g. Johnson et al., 1999, Armstrong et al., 2000). Specifically the distinct peaks in the region between 3100 and 2800 cm-1 are a sign of a possible treatment. An unambiguous identification of the type of treatment purely on spectroscopic data is however considered very hard, because of the numerous filling substances, all showing their presence in this region, and the presence of mixtures, when two or more treatments have been applied.

Contamination by air is normally taken into account, but for the record a spectrum of air (absorptions mainly due to H2O and CO2) is depicted in Figure 4.6a. Figure 4.6b shows absorptions due to contamination from

30 unwanted organic material sticking on the outside of gems (by human contact, etc.), here on a typical diamond spectrum. This results in artefacts at 2957, 2919 and 2850 cm-1: this is in the same range as where treatments are detected. Although we cleaned the samples before measuring, a part of it may still be present.

Figure 4.6. a) Contamination by air. Peaks are due to H2O and CO2. b) Typical diamond spectrum: absorption peaks in the black box are due to external organic contamination (“filthy fingers”). 4. 2. Observations and interpretations

4.2.1. Step 1: blind classification

A first classification was done separately for UV-VIS and IR by comparing the spectra on curve morphology differences without any foreknowledge about meaning of the spectra (as seen in the previous chapter), thus preventing any influence of biases. We could discriminate five main UV-VIS groups with significant differences (Table 4.4 and Table 4.6). The fifth group contains only a single spectrum. The four other groups could be subdivided in more classes based on minor differences.

The comparison of IR spectra lead to a division into eight groups (Table 4.5 and Table 4.7). Group 8 however comprises only one spectrum, but is indeed significantly different. Although it seems to be an apparent feature, the saturation degree (certain absorption bands may even lead to a saturation of the signal, Figure 4.7) is not considered characteristic, because this is dependent on various factors like gem size, orientation, transparency, inclusion amount. It is also possible that the sample lies in the pathway of only a part of the radiation beam. All these factors are not of interest and/or we don’t take into account in our research.

Figure 4.7. Differences in saturation. Below: detector saturation is reached.

A major difficulty we encountered is the discrimination of certain small peaks we included in the classification. Especially the triplet or quadruplet found regularly between 3100 – 2800 cm-1 may therefore require a sometimes subjective decision. Moreover, the exact positions of the peaks in that region differ a lot (Figure 4.8), and they may match the peaks due to external organic contamination (Figure 4.6). Because of the rather exploring goal of this first classification, we only limit our discrimination to a “present” or “absent” for this range.

Figure 4.8. Detail of three FT-IR spectra (top to bottom: GE03385G, GE8330G, GE03462G) illustrating the problems of the 3100-2800 cm-1 region. (a) Are the peaks of the middle spectrum significant and what is the influence of external contamination? (b) If significant, is the difference in WN significant?

In Table 4.3 we compare the two classifications to observe any correlations. UV-VIS group 2 and IR group 6 match completely: the characteristic absence of an absorption peak at 985 nm appears to be characteristic, as is the lack of absorptions in the NIR and MIR between 7000 - 2000 cm-1. The other main groups, UV-VIS 1+3 and IR 1 + 2, don’t show clear relations, although all but one samples are comprised in these groups. The smaller IR groups 3 and 7 are included by UV-VIS 1; IR 5 by UV-VIS 3. The single spectrum in group UV-VIS 5 belongs to a trapiche emerald, explaining its apart classification. It is however interesting that the matching IR spectrum

32 belongs to the second largest group, suggesting that a large amount of inclusions does not necessarily influence the IR region significantly. Single spectrum group IR 8 matches with a small UV-VIS group (4), indicating that this may be a special species indeed. Group IR 4, having the same characteristics as IR 2 except for its lack of the 2350 cm-1 peak, shows also no clear correlation.

Table 4.3. UV-VIS and IR group comparison.

Number of emeralds / group IR class. 1

UV-VIS class. 1 1 2 3 4 5 6 7 8 Total

1a 5 8 13 1b 5 8 2 15 1c 20 6 4 1 31 1d 5 5 2a 7 7 2b 6 6 2c 2 2 2d 1 1 3a 12 6 2 20 3b 6 2 8 3c 11 2 13 3d 8 8 4a 1 1 4b 2 2 5 1 1 Total 64 33 4 3 10 16 2 1 133

Conclusion of this first inspection: without further background knowledge of the meaning of the distinctive features of the UV-VIS and IR spectra, a determination is certainly not self-evident. However, the 958 nm absorption peak and the absence of certain broad absorptions in the infrared region already appear to be of interesting value. Other determining features will have to show their significance in the next chapter, where we will make a new classification based on a combination of both UV-VIS and IR.

Table 4.4. 1st UV-VIS classification of emerald groups (+ = present; - = absent; gray field = not possible to determine (N/A) or not included for the classification; bold frame = main characteristic feature).

wavelength Group 1 Group 2 Group 3 Group 4 Group 5 Feature (nm) a b c d a b c d a b c d a b absorption absorption trough trough 325-400 Transmission band around slope slope around + + 370 - rather + + + + + rather + 370 + Reduced Main Top than band 340 - 350 ~325 than band 340 - 350 absorption trans- Main band with top ~510 + + + + + + + + + + + + + + bands mission No Low bands Main band with top ~700-740 transmissi transmissi 700 - 710 710 - 740 710 - 740 700 - 710 on on

Main band with top ~1030 + + + + + + + UV - V I S I V - UV 680-1100 + + +, No real + + + + + Broad tabular band top: 730-740 + + top + + + + + Small absorption Small 681-684 doublet + + + + + + + + + peaks Small absorption 958 + + + + - - - - + + + + -

Table 4.5. 1st IR classification of emerald groups (+ = present; - = absent; bold frame = main characteristic feature).

wavelength Feature Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7 Group 8 (cm-1) Explicit slope 7000-6000 ------+ Explicit absorption peak 5500-5000 + + + + + - - +

Strong absorption band 4000-3200 + + + + + - - + Significant absorption Peaks 3000-2800 + - + - + - - - peak triplet and 5-6 explicit absorption bands 3000-2400 - - - - + - - -

F T - I R I - T F bands and peaks Significant peak doublet 2600-2400 - - + - - - - -

Explicit absorption peak 2350 + +/- + - + - - - Strong absorption band 2000-400 + + + + + + - +

Table 4.6. UV-VIS classification 1 of our samples.

1a 1b 1c 1d 2a 2b 2c 2d 3a 3b 3c 3d 4a 4b 5 GE03388G GE03385G GE03387G GE03601G GE03406G GE03405G GE03400G GE03403G GE03382G GE03378G GE03428G GE03376G GE03402G GE8330 GE9901G GE03389G GE03386G GE03396G GE03612G GE03409G GE03407G GE03401G GE03404G GE03430G GE03379G GE03429G GE03377G GE8609G GE03391G GE03390G GE03397G GE03613G GE03411G GE03408G GE03431G GE03380G GE03434G GE03542G GE03394G GE03399G GE03422G GE03614G GE03412G GE03410G GE03432G GE03381G GE03435G GE03543G GE03395G GE03420G GE03452G GE8986G GE03414G GE03413G GE03433G GE03383G GE03436G GE03546G GE03398G GE03421G GE03453G GE03416G GE03415G GE03439G GE03384G GE03438G GE03547G GE03417G GE03423G GE03454G GE8608 GE03443G GE03437G GE03440G GE03548G GE03418G GE03424G GE03455G GE03444G GE03638 GE03445G GE03551G GE03419G GE03602G GE03456G GE03449G GE03446G GE03552G GE03425G GE03615G GE03457G GE03450G GE03447G GE03462G GE03635 GE03458G GE03451G GE03448G GE03600G GE03636 GE03459G GE03540G GE8989 GE08324 GE03637 GE03460G GE03541G GE9308 GE03639 GE03461G GE03545G GE9324 GE03640 GE03463G GE03550G GE08502 GE03464G GE9255 GE03465G GE9317 GE03466G GE9321 GE03467G GE9322 GE03468G GE9323 GE03469G GE9326 GE03470G GE9331 GE03471G GE03472G GE03473G GE03474G GE03475G GE03476G GE03477G GE03478G GE03544G GE9088

Table 4.7. IR classification 1 of our samples.

1 1 2 3 4 5 6 7 8 GE03378G GE03463G GE03433G GE03478G GE03544G GE03547G GE8608 GE03637 GE03402G GE03380G GE03464G GE03425G GE03457G GE8330 GE03545G GE03412G GE03640 GE03381G GE03465G GE03462G GE03452G GE8609G GE03550G GE03410G GE03382G GE03466G GE03602G GE03453G GE03376G GE03400G GE03383G GE03467G GE03472G GE03546G GE03414G GE03384G GE03468G GE03430G GE03551G GE03401G GE03385G GE03469G GE03476G GE03548G GE03409G GE03394G GE03470G GE03638 GE03542G GE03404G GE03395G GE03474G GE03541G GE03543G GE03411G GE03396G GE03475G GE03639 GE03552G GE03405G GE03397G GE03477G GE03391G GE03413G GE03418G GE03540G GE03431G GE03406G GE03423G GE03600G GE03417G GE03415G GE03428G GE03601G GE03432G GE03407G GE03429G GE03612G GE03420G GE03408G GE03434G GE03613G GE03422G GE03416G GE03435G GE03614G GE03399G GE03436G GE03615G GE03471G GE03437G GE03635 GE03440G GE03438G GE03636 GE03389G GE03439G GE08324 GE03445G GE03443G GE8986G GE03398G GE03444G GE8989 GE03379G GE03446G GE9308 GE03421G GE03447G GE9317 GE03449G GE03450G GE9321 GE03473G GE03451G GE9322 GE03386G GE03454G GE9323 GE03419G GE03455G GE9324 GE03387G GE03456G GE9326 GE03390G GE03458G GE9901G GE03459G GE03424G GE03460G GE03388G GE03461G

4.2.2. Step 2: classification based on reference samples

By making a new classification based on both UV-VIS and IR spectra of the references, we hope to find out what might actually be the determining features of Table 4.4 and Table 4.5 above. All reference samples are listed in Table 4.8. They represent four different provenances of natural emerald: Colombian, Brazilian, Indian and Zambian. Other important sources as the Madagascar and Sandawana emerald are not incorporated. Further, a series of both flux and hydrothermal synthetic emeralds are included in the dataset. Note that, because investigation on emerald provenance still cannot bring 100 % definite answers, for some emeralds in the dataset, the origin is unknown. Additionally, treatments are not always (correctly) reported in the database, mainly because not all emeralds have been tested for their presence or exact composition. Opticon is the only listed treatment and we got guarantee of its presence in the two given reference samples.

Table 4.8. Reference samples of the dataset.

Sample nr. Natural / Provenance / type Treatment UV-VIS class. 1 IR class. 1 Synthetic GE03388G Nat Brazil 1a 2 GE03389G Nat Brazil 1a 2 GE03378G Nat Colombia 3b 1 GE9317 Nat Colombia Opticon 3a 1 GE9326 Nat Colombia Opticon 3a 1 GE8986G Nat India 1d 1 GE03473G Nat Zambia 1c 2 GE03475G Nat Zambia 1c 1 GE03400G Syn Flux 2c 6 GE03409G Syn Flux, Chatham 2a 6 GE03415G Syn Flux, Chatham 2b 6 GE8330 Syn Hydrothermal, 4b 4 Lechleitner GE8609G Syn Hydrothermal, 4b 4 Lechleitner

a) Evaluation of classification 1

We can use this list first to evaluate classification 1. A first observation is that all reference samples from equal origin were previously categorised into the same UV-VIS groups. Groups 1 and 3 appear to belong to the natural forms, while 2 and 4 represent the flux and hydrothermal synthetic varieties. The references also support a part of the IR classification: the flux and hydrothermal synthetic ones match groups 6 and 4 respectively. All natural emeralds have been categorised into IR groups 1 & 2. The main

37 feature that defined those two groups is the presence or absence respectively of the peaks in the 3100- 2800 cm-1 region. However, as seen in a previous chapter, this IR region is actually indicative for the presence of treatments. Based upon these observations we can already suggest two hypotheses: (1) The incorporated synthetic and natural emeralds appear to have distinct differences in both regions, and (2), our IR classification in no way discriminates between the different natural origins, while the UV-VIS grouping may contain significant elements.

b) Classification 2

Our new classification (from here on also referred to as “Class2”) will be based upon both UV-VIS and IR, and upon the literature discussed in § 4. 1. A good tactic would be to classify upon UV-VIS spectra because of its more detailed subdivisions, to subsequently observe any relations in the IR spectral features. The first step is to put the spectra into some kind of numeric form in order to simplify classification with dataset processing software (in view of its obvious origin, from here on we exclude the trapiche form, sample GE9901G). Each feature and its state we consider valuable, based both upon literature and our own observations, is examined for each individual spectrum. This leads to a table with 19 UV-VIS and 20 IR features listed for our 132 minerals (appendix 7. 3). In the UV-VIS part, both transmission (Tr) and absorption (Ab) maxima are presented, starting with the broad bands (B) followed by the smaller peaks (P) and shoulders (S). The subsequent IR region gives all absorption bands, peaks and shoulders.

In the UV-VIS region, we distinguish two types of features: (a) The first one handles the presence and state of a feature. There are four main states: “0” when it is absent, “++” for a very distinctive feature, “+” means it is present and distinctive, “-“ says it is present, but only minor. The “N/A” state is received when it is impossible to make an observation. A “+” state for feature “Tr B1 325-400” for example means that transmission band 1 between these wavelengths (in nm) is apparent, but certainly not dominant. The first feature in the low UV, “250-325 highest”, means that transmission between these wavelengths is highest of the whole spectra. Note that the assignment of a character state may be subjective: it is based on the feature’s relation to other features in the same spectra compared with the other spectra. (b) The other type describes the absolute minimum or maximum of a feature and is purely objective. “N/A” means the feature is not or only in a minor way present; “plateau” means a transmission band is present, but has no clear maximum.

In the IR region, the same classification is used for type (1), although following remarks have to be made: “++” means that signal saturation is reached, while “+” means it is present and distinct, without saturation. “N/A” means that the signal is too noisy or saturated to clearly observe a feature. The maximum is always presented above; when it varies, it is mentioned in the table. For two features the form is also examined.

We listed and explained these abbreviations and symbols also in appendix 7. 1.

The results of classification 2 are presented in column 7 to 9 in Table 7.4 in appendices. This is recapitulated in Table 4.9, where feature states are given for each provenance. The bordered cells are the feature states that we think are characteristic for a certain origin. The results will be discussed in the next chapter (4. 3 and 4. 4), after we compare them with the complete dataset. This way we can be sure we discuss the right origins, leading to higher quality and a reduced chance to repeat ourselves.

Table 4.9. Classification 2: all UV-VIS and IR characteristics of what could be a typical emerald of a particular source. Black borders surround the determining characteristics of Class2. B = band, P = peak, S = shoulder. Symbols (+,++,-,0,...) are described in text.

UV-VIS (nm)

450 650 875

372

400 525 800

478

- - - -

est ? est

325 325 high

Min 1 Min 2 Min 3 Min

683/4

Max1 Max2 Max3

B2 475 B2

Ab S3 S3 Ab 636 S4 Ab 660

Ab P6 Ab 957

Ab P5 Ab 681 &

250

Ab S2 S2 Ab 476

Tr325 B1 Tr Tr650 B3

Ab P1 Ab 370

Ab B1 B1 Ab 400 B2 Ab 550 B3 Ab 800

Emerald provenance Emerald Treated?

COLOMB y/n 0 ++ 350 ++ 430 ++ 505 ++ 610 ++ 750 - N/A 0 + + + + ++ BRAZ y/n 0 + 380 ++ 430 ++ 510 ++ 610 ++ 710 ++ 840 0 + + + ++ - ZAM y/n + + 385 ++ 430 ++ 510 ++ 610 + 730 + 840 ++ 0 + 0 ++ + INDIA y/n 0 0 370 ++ 430 ++ 515 ++ 615 ++ 735 + 840 0 0 + + ++ + FLUX 1 n 0 + 350 ++ 430 + 505 ++ 605 ++ 730 - plateau 0 0 + -/+ + 0 FLUX 2 N 0 0 N/A ++ N/A ++ 530 - 605 ++ 740 - N/A 0 0 + 0 - 0 HYDRO 1 n 0 ++ 355 ++ 430 ++ 505 ++ 605 var. var. 0 N/A 0/+ 0/+ + + ++ ++ HYDRO 2 n 0 ++ 345 ++ 430 ++ 505 ++ 605 ++ 780 0 N/A 0 0/+ + 0/- ++ ++

IR (cm-1)

4000 2800

- -

5600 5100 3400 2300 3115 2323

t S t 5400

Ab zone Ab

Ab S Ab 2443 S Ab 2475

Ab P P Ab 6817 P Ab 2291

Add. left Add. S

4400 3000

6 P/Bs 6 3100

Lef S Left 2372

Add. right Add. S

Right S RightS 5100 RightS 2339

Form5273 P

FormRight S

Large5273 P

- P Ab 3235 Large2359 P

BroadB4000

Smallplatform

Ab Ps Ps Ab 3165 and

Emerald provenance Emerald 5

COLOMB + 0 + + fine + round 0 ++ 0 + + +/0 0 + + ++ + 0 + BRAZ + + 0 ++ triangle 0 0 0 ++ 0 + +/0 +/0 0 0 + ++ + 0 + ZAM + + 0 ++ triangle 0 0 + ++ 0 0 +/0 +/0 0 2470 + ++ + 0 +

INDIA + + 0 + triangle 0 0 0 ++ 0 0 +/0 +/0 0 0 + + 0/+ 0 0/+ FLUX 1-2 0 0 0 0 0 0 0 0 0 0 0 3220 0 + 0 0 0 0 + 0

HYDRO 1 + 0 + + fine + round ++ ++ 0 + 3220 0 + 0 0 0/- 0 + 0

HYDRO 2 + 0 + + fine + round ++ ++ 0 - 0 0 2450 0 0 0 0 + 0

4.2.3. Step 3: Comparison with the dataset of HRD Antwerp

a) The dataset

Dataset information on provenance or synthetic type of all emeralds is presented in the last 4 columns in Table 7.4 in appendix 7. 3. The comparative table below (Table 4.10) makes it somewhat more illuminating. As one can see, not all origins had been specified yet: Madagascar, Sandawana (Zimbabwe) and South-African emeralds are also included in the dataset. A subdivision in synthetic Chatham, Lennix and non specified flux emeralds is Also included. The hydrothermal variant comprises the Lechleitner, AGEE and a non-specified group. To spice things up even more, there are also 8 emeralds from unknown origin. Further ahead in this chapter we will examine if we can assign them to one of the given provenances. Before we discuss the different origins, first, a little evaluation of our classifications.

Table 4.10. Comparison of classification 2 with the dataset.

Number of spectra / group Dataset Origin

Match ?

AGEE Lechleitn

- -

Africa

Lennix

Chatham

- -

Class 2 Class 2

Brazil Colombia Flux Flux Flux Hydroth. Hydroth. Hydroth. India Madagascar Sandawana South Zambia Total code origin YES NO ? 1 Col 36 36 36 2 Bra 11 17 5 11 9 1 1 1 28 3 India 1 8 3 1 5 9 4 Zam 26 3 3 26 29 5a Flux1 15 4 10 1 15 5b Flux2 1 1 1 6a Hy1 3 1 1 2 1 4 6b Hy2 10 1 9 10 Total 103 29 8 14 36 6 10 1 1 2 10 1 9 6 1 27 132

b) Comparison with classification 2

We have already assigned 103 of the 132 emeralds to the correct origin, from which 74 to their right natural provenance and 29 to their right synthetic type. We consider synthetic emeralds as correct when

41 assigned correctly to flux or hydrothermal; the only inconsistency is one hydrothermal synthetic (GE03402G) that actually should be flux-grown, but all synthetic emeralds were distinguished form their natural counterparts. Colombian emeralds, categorised in group 1 are the only natural emeralds with a 100 % detection success rate. Also, only 4 of the 27 Zambian emeralds have been falsely grouped: 3 appear to be Brazilian, while 1 “Brazilian” comes out to be Zambian. We cannot yet conclude anything about the classification of groups 2 (Brazil) and 3 (India): they comprise also the newly added groups. In the next chapter, a deeper motivation of this classification and the mismatches is given after each origin.

c) Comparison with classification 1

How successful was our first blind classification (from here on also referred to as “Class1”) actually? The flux minerals were all discovered, both in UV-VIS (2a-b-c) and IR, except for that same inconsistency from Class2: this emerald actually matches single spectrum group Class1-IR-8: our presumptions about the importance of the distinctive lack of H2O related features and the “special case” state of group IR 8 appear to be correct. Hydrothermal synthetics are all classified in IR 4-5, that are both characterised by

-1 the lack of a large (CO2 related) peak around 2350 cm and, only valid for group IR 5, a series of peaks in 3000-2500 cm-1. Confirming our suggestions, all natural emeralds where classified in IR groups 1-2, although it incorporates also one hydrothermal synthetic emerald (GE8330G). These are the most important trends; other issues will be discussed in the next chapter for each origin apart.

4. 3. Spectroscopic features of natural emeralds

The general emerald UV-VIS and IR spectra have been explained at the beginning of this chapter. Here we list the specific spectroscopic characteristics typical for each origin we observed in our set and we complement them with information of existent literature. All observations and ranges for each origin are given in appendix 7. 2, observations for particular spectra in appendix 7. 3. Symbols and abbreviations are similar like Class2, and are explained in appendix 7. 1. We refer back to Table 4.9 (p. 40) for the characteristics of the groups in classification 2. For each origin, we also give the ID’s of the spectra like they are listed in the dataset of HRD Antwerp.

4.3.1. Colombia

Dataset: 36 emeralds GE03378G GE03379G GE03380G GE03381G GE03382G GE03383G GE03384G GE03428G GE03429G GE03430G GE03431G GE03432G GE03433G GE03434G GE03435G GE03436G GE03437G GE03438G GE03439G GE03440G GE03443G GE03444G GE03445G GE03446G GE03447G GE03449G GE03450G GE03451G GE03540G GE03541G GE9317G GE9321G GE9322G GE9323G GE9324G GE9326G

a) UV-VIS

In the NIR region between 800 and 900 nm, determined by the presence of Fe2+, Colombian emeralds show very low absorption (Figure 4.9). This leads to a quasi-tabular form between the two broad transmission bands (seen in all emeralds) at ~ 700 and at 1000 nm. This feature is responsible for the presence of a red fluorescence (§ 2.2.2, p. 5), commonly seen in Colombian and synthetic emeralds. Another typical feature is the mean maximum of the first transmission band, which is at the lowest wavelengths of all natural emeralds, at 350 nm (in 27 out of 36 cases) until max. 370 nm (in 2 cases). Also the position of the maximum of band 2 is in 32 cases lower than other naturals (505 vs. 510 nm); transmission band 3 has a higher range with 28 cases between 740 and 750 nm. All these features have however also been spotted in flux and some hydrothermal synthetic forms (see § 4. 4). The strong H2O peak at 957 nm is yet a very characteristic feature to distinguish Colombian from these synthetic emeralds, and even from other natural forms.

Figure 4.9. UV-VIS spectrum of a typical Colombian (GE03381) and Brazilian emerald (GE03388), showing the obvious difference between 780 and 1000 nm due to a different Fe2+ amount.

b) IR

Typical is the region between 5500 – 5000 cm-1 (Figure 4.10). This shows a sharp peak at 5273 cm-1 surrounded by two rounded shoulders at 5450 and 5100 cm-1, pointing to a low alkali content. Especially the left round shoulder is expressed. We have discovered this typical triplet in Colombian emeralds, in all but two5 cases, and for the rest in only one6 Brazilian emerald spectrum. Caution is required, though, because this feature is also present in hydrothermal synthetic emeralds. The range around 2359 cm-1 typically reveals a broad absorption band: in 2 cases on 3 it even overwhelms the two shoulders that are normally observed in other natural emeralds (also seen on Figure 4.10). The peak around 2475-76 cm-1, found in all but four7 Colombian emeralds may also be an additional characteristic feature (32/36 spectra), although we also observed the same6 Brazilian emerald showing it. This is still a distinctive feature compared to some Brazilian and Zambian emeralds showing absorption between 2470-72 cm-1. Another feature that may help the identification is the presence of absorption shoulders around 3165 and 3115 cm-1 not seen in synthetic emeralds.

Figure 4.10. Details of the IR spectrum of typical Colombian emeralds. Left (GE03379G): the typical fine 5273 cm-1 peak and rounded shoulders. Right (GE03381G): characteristic absorption peaks in the 3400 – 2000 cm-1 range.

5 GE03430G, GE03439G 6 GE03385G 7 GE03378G, GE03380G, GE03382G, GE03450G 44

a) Classification and comparison with dataset

As mentioned, all 36 Colombian emeralds were detected in the second classification and were even already considered in the same UV-VIS group (3a-b-c) in the first blind classification based on their low absorption around 830 nm. However, some hydrothermal emeralds, one Zimbabwean and one South- African variety where also grouped in UV-VIS 3a-b-c, but after thorough comparison, the latter two appear to have still distinct absorption in that region.

Figure 4.11. Comparative figure of FT-IR spectra of representative emeralds of all examined origins.

4.3.2. Brazil

Dataset: 14 emeralds GE03385G GE03386G GE03388G GE03389G GE03390G GE03391G GE03394G GE03395G GE03398G GE03399G GE9308G GE03387G GE03396G GE03397G

a) UV-VIS

The high Fe2+ amount that accompanies the Brazilian emeralds (§ 0, p. 14) explains the large (very distinct though not always complete) absorption band at 840 nm (Figure 4.9) seen in all cases. The transmission band between 325-400 nm is rather modest, certainly in comparison with Colombian variants, and sometimes even absent. Only three8 spectra show a very distinct transmission band. These spectra also show the Fe3+ absorption trough in the middle of this range. Unique (combinations of) characteristics were however not found for Brazilian emeralds. We can say though that, indicated by the Cr peaks (636, 660, 681-84 nm), no Cr-free emeralds, typical for some Brazilian deposits (Wood and Nassau, 1968), are present.

b) IR

Figure 4.11 depicts IR spectra of all examined origins. Brazilian emeralds don’t show (except for one6) the rounded shoulders around the 5273 cm-1 peak. Instead one “triangular shaped” peak appears, pointing to a higher alkali content. Also the 2475 cm-1 peak doesn’t show, but three8 emeralds show instead a peak at 2472 cm-1. The IR spectrum of Brazilian emeralds has all in all actually no real determining characteristics. Maybe a minor feature we observed, is the absence of a little plateau between 4400 and 4000 cm-1 in most of the Brazilian spectra, which occurs in most other origins.

c) Classification and comparison with dataset

In classification 1 Brazilian emeralds belong to group UV-VIS 1 (a-b-c): this group is based on the strong absorption between 800 and 900 nm and contains emeralds from all other groups as well (except Colombian). In classification 2 (group 2), this same feature is used in combination with absence or absence of smaller features in the UV-VIS (no absorption at 370 nm) and IR (no peak at 3245 cm-1). But as mentioned, after dataset comparison came out that this group contained also three Zambian emeralds

8 GE03387G, GE03396G, GE03397G 46

(the ones already mentioned in footnote 8) and the newly added origins, then yet still unknown to us. Indeed, the Brazilian and other emeralds yet to come are harder to differentiate.

4.3.3. Zambia

Dataset: 27 emeralds GE03452G GE03453G GE03454G GE03455G GE03456G GE03457G GE03458G GE03459G GE03460G GE03461G GE03462G GE03463G GE03464G GE03465G GE03466G GE03467G GE03468G GE03469G GE03470G GE03471G GE03472G GE03473G GE03474G GE03475G GE03476G GE03477G GE03478G

a) UV-VIS

All but two Zambian spectra (Figure 4.12) show a distinct Fe3+ band around 370 nm, consistent with the high Fe3+ content mentioned in § 0, p. 14 (Zwaan et al., 2005). Most of the Zambian emeralds are also characterised by a high transmission in the UV zone between 250 and 325 nm: this band is higher than the rest of the transmission bands, in 26 to 1 cases. Zambian emeralds have further a distinct but not a complete absorption around 840 nm. Another feature that may indicate a Zambian origin is the frequent presence (15 cases) of the high wavelength (730 nm) of transmission maximum 3, that is mostly higher than Brazilian, Indian, South-African or Madagascar emeralds. One example9 is really different, lacking the 372 nm absorption band and the high intensity UV band, and showing complete absorption around 840 nm.

a) IR

The 5500-5000 cm-1 part of the IR spectrum of Zambian emeralds (Figure 4.11) is not much different than a mean Brazilian. The plateau between 4400 and 4000 cm-1 is more often present (25/27 cases), and 21/27 cases lack the 3235-45 cm-1 band. A typical feature is a peak around 2470-72 cm-1, different from the Colombian 2475 cm-1 peak. The peak around 2340 cm-1 was not present in four cases10. Four11 cases show a very strong absorption doublet between 2600-2400 cm-1 (Figure 4.13); the cause remains unknown.

9 GE03462G 10 GE03467G, GE03468G, GE03470G, GE03474G 11 GE03452G, GE03453G, GE03457G, GE03478G 47

Figure 4.12. Typical UV-VIS spectra of Zambia (GE03478G), India (GE8986G), Madagascar (GE03417G), Zimbabwe (GE03640G) and South-Africa (GE8989G).

Figure 4.13. Detail of an IR spectrum of a Zambian emerald (GE03453G) that shows distinct absorption features between 2600-2400 cm-1.

b) Classification and comparison with dataset

Zambian emeralds have since the blind classification (group 1c) and the 2nd classification been defined by their strong absorption around 370 nm due to Fe3+. Although it might give a nice clue, we may not consider this feature characteristic. Three8 Brazilian spectra also show this for example, but literature (Zwaan et al., 1997, Wood and Nassau, 1968) is also clear that this feature is certainly not unique. The 48 mentioned specrum9 with Brazilian characteristics, is already an example of the limitations of the UV-VIS origin detection capabilities. Also one spectrum has been wrongly classified Zambian12 because of doubt about these same features.

In Class1, we based group 3 on strong absorptions between 2600 and 2400 cm-1, but ignored this feature (correctly) in Class2.

4.3.4. India

Dataset: 1 emerald GE8986

a) UV-VIS

With only a single spectrum it is not possible to find trends. Literature about spectroscopic properties is also limited (we couldn’t get our hands on it), because this is a recent discovery and exploitation. But as mentioned, some southern Indian emeralds have been found with similar physical properties, composition and inclusions as their counterpart from Madagascar (Panjikar et al., 1997). It might therefore be interesting to look closer for similarities there. Anyway the features are not significantly different than in some Brazilian spectra, with high absorption between 350 and 430 nm and around 830 nm. The only feature that might be interesting is the lesser absorption maximum around 615 nm, that we have only seen yet in one Colombian emerald13.

b) IR

This single spectrum is characterised by extreme H2O and CO2 related absorptions. Slight 3165 and 3115 cm-1 bands have been observed.

c) Classification and comparison with dataset

This last group of natural emeralds in classification 2 consisted actually of spectra that are from Sandawana or unknown origin. This was indeed an artificial classification with less convincing features as exact position of transmission bands as similar characteristic.

12 GE03469G 13 GE03429G 49

4.3.5. Madagascar

Dataset: 9 emeralds GE03417G GE03418G GE03419G GE03420G GE03421G GE03422G GE03423G GE03424G GE03425G

a) UV-VIS

Emerald spectra of Madagascar all show a very sharp and high transmission band around 510 nm. Other transmission bands may vary. Some cases14 show a transmission peak at 700 nm, which is the lowest (in wavelength) we have observed in the whole set. But in general, spectra are not significantly different than some Brazilian or Zambian emeralds. One example15 even shows a very distinct Fe3+ peak at 370 nm, consistent with the findings of Schwarz (1994) that this iron form may be present. The comparison with the Indian spectrum does not work out: a transmission band around 375 nm is present and a significant lower absorption around 610 nm is seen only once16. The comparison with Indian spectra is not relevant.

b) IR

The spectrum is very similar to the most examined Brazilian spectra. The comparison with Indian spectra is again not relevant.

c) Classification and comparison with dataset

All spectra were classified (Class2) as from Brazilian origin, because of their large absorption band around 840 nm and because presumed Zambian and Indian features were not present.

4.3.6. Sandawana (Zimbabwe)

Dataset: 6 emeralds GE03635G GE03636G GE03637G GE03638G GE03639G GE03640G

a) UV-VIS

Five17 of the six spectra (Figure 4.12) show very high and sharp (++) transmission bands around 375, 515 and 730 nm. The form and size of this first feature is barely seen in Brazilian emeralds, the second not

14 GE03417G, GE03418G, GE03425G 15 GE03422G 16 GE03425G 17 GE03636G, GE03637G, GE03638G, GE03639G, GE03640G 50 always in Brazilian and Zambian, and the third is never that high in Zambian species. They also show only weak Fe2+ absorption in the 850 nm region, and absorption is even almost absent in one case18. Colombian emeralds can still easily be distinguished from such cases by the presence of the very distinct 958 nm peak. The other spectrum19 however doesn’t show these features, thus revealing a Brazilian-like spectrum: low 375 and 730 nm transmission bands and high absorption around 840 nm. This indicates again that an unambiguous distinction with other deposits cannot be made based upon UV-VIS spectra. None of the spectra shows a distinct proof of the 372 nm Fe3+ absorption band.

Figure 4.14. Detail of IR spectra of Zimbabwean emeralds. From top to bottom: less relief, probably due to bad measurement.

b) IR features

The Zimbabwean emeralds contain three20 spectra showing a less detailed spectrum, from which one21 is even completely flat (Figure 4.14): comparing with Figure 4.6 on contamination of air, this is probably only due to bad measurement: the infrared beam probably (partly) missed the sample. Anyhow, the

-1 other spectra show a typical extreme triangular 5500-5000 cm H2O band (compare with other origins in

18 GE03638G 19 GE03635G 20 GE03635G, GE03637G, GE03640G 21 GE03640G 51

Figure 4.11). Also, the left shoulder at 5600 cm-1 is very expressed. The 2291 cm-1 peak is in none of the cases very expressed and even absent in two22 cases.

c) Classification and comparison with dataset

The five17 spectra were previously categorised in Class2-group-3 (“Indian”), based upon the higher wavelength of the second transmission (515 nm) and absorption (615 nm) maximum. One spectra23 was originally from group 2 (“Brazil”). The “flat spectra” emeralds where discovered in Class-1-IR-7, but are thus not a distinctive characteristic.

4.3.7. South-Africa

Dataset: 1 emerald GE8989G

a) UV-VIS

This new group contains also only one sample, and the characteristics are merely the same as previous origins, so there’s not much to say: it’s not Colombian, it’s certainly not synthetic (see § 4.4.1), and probably not from Zambia (no Fe3+ absorption), Madagascar and Zimbabwe (510 nm peak is not that sharp and large).

b) IR

Two significant differences are the lack of the 2293 cm-1 peak, but this is anyway not representative, considering having only a single spectrum.

c) Classification and comparison with dataset

In Class2, we originally classified it “Brazilian”. In Class1, the not complete Fe2+ absorption lead to the subjective assignment to group UV-VIS-3c, similar to all Colombian specimens.

22 GE03635G, GE03637G 23 GE03635G 52

4. 4. Spectroscopic features of synthetic emeralds

4.4.1. Natural versus synthetic flux versus synthetic hydrothermal emeralds

Research on synthetic emerald has already been performed since the late sixties. It is easy to recognise flux-grown emeralds, because until now, it is not possible to introduce water into the structure of flux- grown emeralds: this leads to the absence of any peaks and bands in UV-VIS and IR spectroscopy related to water (Wood and Nassau, 1968, Stockton, 1987).

Hydrothermal emeralds are harder to recognise. The UV-VIS spectra may vary a lot, and will be explained apart for each type. The IR region does show a few trends. Some types have a series of strong absorption features between 3000-2500 cm-1. Some natural emeralds may show some of these features in some degree, but never all together nor with a comparable magnitude. Schmetzer et al. (1997) attributed these bands to chlorine. Another feature is the presence of peaks at 3295 cm-1 and 3232 cm-1:

+ Mashkovtsev and Solntsev (2002) assign this to ammonium (NH4 and NH3 respectively). Other types don’t show them, but fortunately, there are also features in the 2400-2200 cm-1 range that discerns them from their natural counterparts: most natural emeralds normally show a large peak at 2357 cm-1 with a left shoulder around 2340 cm-1, and a peak at 2291 cm-1. In synthetics, this last peak has, until recently never been observed, the 2340-shoulder is “moved” to around 2320 cm-1, and the 2357 cm-1 band is mostly absent or reduced. Exceptions may however show a (reduced) 2357 cm-1 peak (Stockton, 1987). Recently an example of a Tairus hydrothermal emerald has been found that showed the 2291 cm-1 peak (Duroc-Danner, 2006). Between 5500 and 5000 cm-1, all synthetic emeralds show rounded shoulders around a fine peak, some more extremely than others, pointing to a low content or absence of alkalis. In non-polarised spectra like ours, this feature is not distinguishable from low-alkali natural (typically Colombian) forms (Schmetzer et al., 1997). Table 4.11 lists synoptically the IR characteristics we brought up.

Table 4.11. IR features that discerns synthetic from natural emeralds (references in text).

Feature Natural Synthetic Fine 5273 cm-1 peak and rounded Present only in low-alkali forms (usually Present shoulders Colombian) Series of 5-6 peaks-bands at 3000- Almost not, or very minor Strong, or absent 2500 cm-1 -1 2357 cm CO2 peak Mostly present Mostly absent, sometimes minor -1 -1 Right CO2 shoulder Around 2340 cm 2310-2330 cm 2291 cm-1 Mostly present Absent (?)

4.4.2. Hydrothermal synthetic emeralds

A list of the important hydrothermal synthetic emerald producers was already given in Table 2.6, p. 15. Here we discuss their spectroscopic features that may help to distinguish them from each other. The features are given in appendix 7. 2.

a) Lechleitner

Dataset: 2 emeralds GE8330G GE8609G The Lechleitner hydrothermal emerald is Cr and Cu based. Its spectra are depicted in Figure 4.15. The UV-VIS spectrum is characterised by very strong, very sharp transmission bands around 355 and 505 nm, but a lack of a transmission band around 700 nm. Moreover, total absorption occurs at 760 nm, proving that Cu2+ is abundantly present (§ 4.1.1, p. 27). The IR spectrum doesn’t show the peaks between 3000- 2500 cm-1, but does have the other typical hydrothermal characteristics listed in Table 4.11 above. The middle peak at 5273 cm-1 can be small or large (though is always fine). Two other features are the shoulder around 2443 cm-1, where Colombian natural emeralds show a peak around 2475 cm-1, and a peak around 3220 cm-1, in comparison with some natural emeralds that show a peak around 3235 cm-1. We found no causes for these features in literature.

Figure 4.15. UV-VIS (left) and IR (right) spectrum of a Lechleitner hydrothermal emerald (GE8330G).

b) AAGE

Dataset: 1 emerald GE03376G The AAGE UV-VIS spectrum in Figure 4.16 is like a very pure Colombian spectrum with no absorption around 850 nm. The infrared spectrum shows the absorption series between 3000 and 2500 cm-1; exact positions are listed in Table 4.12. The shoulders around a small 5273 cm-1 peak are very rounded, showing a lack or very low content of alkali’s.

Figure 4.16. UV-VIS (left) and IR (right) spectrum of a AGEE hydrothermal type (GE03376G).

Table 4.12. Exact maxima of the peak series in the 3000 – 2500 cm-1 range in the AGEE IR spectrum.

Feature (cm-1) Band 3020-2950, top around 2980 Peak 2885 Peak 2815 Peak 2750 Band 2675 – 2580, top around 2615

c) Biron

Biron emeralds are the Australian hydrothermal variants and are coloured by both Cr and V. Because we don’t have reference samples anymore about emeralds from this and the following synthetic types, the UV-VIS and IR spectra are only literature based. The UV-VIS spectrum of the Biron synthetic is given in Figure 4.17 and only shows the Cr and overlapping V absorption bands and peaks and is thus again similar to Colombian emeralds.

Figure 4.17. UV-VIS spectra of Biron, Linde-Regency, Malossi and Russian hydrothermal emeralds (after Adamo et al., 2005). 55

A part of the IR spectrum is given in Figure 4.18, showing the distinct series of Cl related bands in the 3000-2500 cm-1 range. These peaks are exactly the same previous Cl-bearing synthetic variants. Other typical features in the 5500-5000 and 2350-2200 cm-1 range are also present, but no ammonium related peaks are observed.

a) b)

Figure 4.18. Datails of non-polarised IR spectra of Biron, Linde-Regency, Malossi and Russian hydrothermal emeralds (after Adamo et al., 2005): a) 9000-4000 cm-1 (our measurements are limited to the black box) and b) 4000-2000 cm-1).

d) Chinese

This type has been produced since 1987 and its chromophore is Cr. We couldn’t get our hands on a UV- VIS spectrum, but Schmetzer (1997) stated that the only absorption bands are due to Cr, producing a Colombian-like spectrum, like the spectra in Figure 4.17 above. He also mentions that the infrared region

-1 contains the typical H2O related features. They also show the distinct Cl bands in the 3000-2500 cm range (Figure 4.19), like previous synthetic emeralds.

Figure 4.19. Detail of a non-polarised IR spectrum of the Chinese hydrothermal emerald compared with the Biron spectrum, showing the Cl related absorption bands and peaks (after Schmetzer et al., 1997). The difference in intensities may be through different orientation of the samples.

e) Linde-Regency

Hydrothermal emeralds were first grown between 1965 and 70 by the Linde Division of Union Carbide Corporation, USA. In ’70, it was sold to Vacuum Ventures Inc. of New Jersey, who produced already the Regency emeralds using similar growth methods (O'Donoghue, 1997). The only agent influencing the UV- VIS spectrum is Cr (Schmetzer et al., 1997), leading to a very similar spectrum as the previous mentioned hydrothermal emeralds, as shown in Figure 4.17. The infrared spectrum (Figure 4.18) reveals Cl-related peaks, but a more characteristic feature may be the ammonium related peaks at 3295 and 3232 cm-1 (Adamo et al., 2005).

f) Malossi

This synthetic emerald, grown in the Czech Republic is only recently (2004) introduced on the market. The UV-VIS spectrum is similar to the previous synthetics (Figure 4.17), with only Cr related bands and peaks (Adamo et al., 2005). The IR spectrum (Figure 4.18) is however very distinctive: the chlorine features are more banded and relative intensities between these peaks/bands are smaller. In addition, they show a very distinct band with top at 3295 and a shoulder at 3232 cm-1, related to ammonium.

g) Russian

Next to the Cr related bands and peaks, the Russian UV-VIS spectrum (Figure 4.17) shows some some other features that distinguish them from the other hydrothermal emeralds brought up so far: it reveals a broad band at about 750 nm related to Cu2+ (see § 4.1.1) as well as an absorption at 372 nm associated

57 with Fe3+. The IR spectrum (Figure 4.18) lacks the 3000-2500 cm-1 bands, and ammonium peaks. It shows a broad absorption band around 8700 cm-1 – out of reach of our measurements – which also has been assigned to tetrahedral Cu2+ (Lebedev et al., 1983).

h) Tairus

Since 1989, this Russian company produces various hydrothermal gemstones, under which of course emerald. Synthetic emerald has earlier been coloured mainly by chromium, but after they took over Biron’s growth technology (typical for the use of equal amounts of Cr and V), the Tairus company created a new version: in 2004, the first synthetic emerald type with negligible Cr content, only coloured by a combination of vanadium and copper appeared on the market. Figure 4.20 shows a polarised UV-VIS spectrum of this new Tairus emerald (as mentioned, our measurements were non-polarised, showing a spectrum that would hold the middle between these two, only little depending on the orientation). The copper absorption band around 750 nm is well observed. The major difference around that band between the two polarised spectra is not completely understood at present. The other marked absorptions are due to V3+. An additional shoulder at 680 nm may be observed. The Cr amount is however very small, so absorption bands and peaks are hidden by the much stronger V bands.

Figure 4.20. Polarised UV-VIS (a) and IR (b) spectra of the new Tairus emerald, between 280 and 800 nm and 820- 2500 nm (12100-4000 cm-1) respectively.

The IR spectrum also shows two Cu2+ features, at 920 nm (10870 cm-1) and 1150 nm (8700 cm-1) (both not in the reach of our measurements). The other marked absorptions are all due to water.

i) Problem cases

Details of the UV-VIS and IR features are presented in appendix 7. 2. Figures of the spectra are reported in the text.

Hydrothermal problem case 1: GE03544G

The dataset contains a sample of unknown hydrothermal origin, GE03544G: we assign a Russian origin to this emerald, based on the following observations (Figure 4.21 and the tables in appendix 7. 2).

 The typical hydrothermal characteristics around 5273 cm-1 are present, as is the absorption pattern in the 2400-2000 cm-1 region: the typical 2325 cm-1 shoulder is spotted, but also an atypical small 2357 cm-1 peak. It lacks the 3000-2500 cm-1 bands.  In addition, it shows Cu2+ related features: the distinct absorption band around 750 nm; in IR, the spectrum even shows the foot of the broad 8700 cm-1 band. Another feature is the 3220 cm-1 peak, we only saw in Lechleitner synthetic emerald.  We assign however a Russian origin, because in the UV-VIS spectrum, the characteristic Fe3+ peak around 370 nm is very distinct.

Figure 4.21. UV-VIS (a) and IR spectrum (b) of hydrothermal emerald GE03544G, assigned Russian synthetic.

Hydrothermal problem case 2: GE03402G

Although the dataset assigns a flux origin for this emerald, we are convinced we should reconsider this case (Figure 4.22). Our motives are as followed.

 We observe the typical spectroscopic bands due to water in the 5500-5000 and 4000-3400 cm-1 range that are not seen in flux-grown minerals.  We are confident to assign a Russian origin again, based on further following evidences.

o No Cl or ammonium features at 3000-2500 cm-1 and at 3295+3232 cm-1 respectively are present. o The infrared spectrum shows further a small peak at 2357 cm-1 and a peak around 3220 cm-1 like in the previous case, as well as the foot of a peak at the lower limit of our spectrum (rising from 6000 to 7000 cm-1). o The UV-VIS spectrum shows a Fe3+ peak at 370 nm and total absorption between 650 and 900 cm-1 related to both Fe2+ and Cu2+.

Figure 4.22. UV-VIS (left) and IR spectrum (right) of hydrothermal emerald GE03402G, assigned Russian hydrothermal synthetic.

Hydrothermal problem case 3: “Hy2”

Hy2: 9 emerald spectra GE03542G GE03543G GE03545G GE03546G GE03547G GE03548G GE03550G GE03551G GE03552G In classification 2, this Hy2 group contained 10 spectra with similar features, from which one appeared to be the AGEE emerald. The UV-VIS shows in all cases a Colombian-like type spectrum (Figure 4.23). The IR shows the series of bands and peaks between 3000-2500 cm-1, although the exact position is not always clear because of signal saturation in three24 cases. The positions of these peaks match with the positions mentioned in Table 4.12, although there are two25 spectra that show the presence of an extra shoulder at 2842 cm-1 and a slightly lower position of the top of the first band (2960 instead of 2980 cm-1). In the 5500-5000 and 2300-2000 cm-1 ranges, they all show the features of Table 4.11 typical for most

24 GE03548G, GE03550G, GE03552G 25 GE03543G, GE03551G 60 hydrothermal emeralds. There are no bands at 3295 and 3232 cm-1, which excludes the Linde-Regency type. They all show a peak around 2450 cm-1 (N/A for the three saturated cases24): we didn’t find it in any other mineral we observed and we have no information on its presence or absence in other non- observed origins. If we don’t consider this feature, the form and combination of the other bands match the, AGEE, Biron or the Chinese type (not Malossi), but based on our spectroscopic measurements, further discrimination is not possible.

Figure 4.23. UV-VIS (left) and IR (right) spectrum of GE03545G, representative for the group “Hy2”.

4.4.3. Flux-grown synthetic emeralds

As mentioned, the separation of flux synthetic emeralds is very easy because they do not contain H2O. In the UV-VIS spectrum, this results in a lack of the 958 nm peak (as seen in Figure 4.24). In the IR spectrum, this leads to a flat spectrum except for the zone between 3000 and 400 cm-1 (Figure 4.11, p. 45). It is logical that we don’t take into account here the proved hydrothermal spectrum GE03402G, mentioned in the previous paragraph.

a) UV-VIS spectrum of Chatham, Lennix and the unknown flux emeralds

To our knowledge, studies of the UV-VIS spectrum of flux emeralds are inexistent. Our dataset contains 10 Chatham, 1 Lennix and 6 emeralds of unknown flux origin. The only absorptions we observe are due to Cr (Figure 4.24). The Lennix and Chatham spectra are all completely similar (details in Table 7.1 in appendices), as is “Unknown3”. The other unknown species, show however some differences: “Unknown2” has only minor absorption around 600 nm, and “Unknown1” and “-2” lack the distinctive higher maximum around 745 nm, seen in all other flux spectra.

a) IR spectrum of flux emeralds

The IR spectrum of flux emeralds has already been investigated (Lebedev et al., 1983) for the most important types, and are given in Figure 4.26. The spectra of the Lennix and the Chatham type are consistent with our data (Figure 4.25), both showing peaks around 2448, 2330 and 2240 cm-1 (the value on the figures may differ a few wavenumbers). Lebedev mentions that the Gilson flux emeralds also have these peaks, and show additional peaks around 2924, 2853 and 2736 cm-1, that are only minor or absent in the other types. We couldn’t get our hands on data of the Taiwan or Russian flux types.

Figure 4.24. UV-VIS spectrum of the 5 discussed flux emeralds.

Figure 4.25. Detail of the IR spectrum of 5 discussed flux emeralds.

Figure 4.26. IR spectrum of Lennix, Chatham and Gilson (after Lebedev et al., 1983).

b) Problem cases

Flux problem case 1: GE03400G and GE03401G (“Unknown1”)

“Unknown 1” shows strong peaks around 2916 and 2849 cm-1. It also shows a shoulder around 2735 cm- 1. This is probably of Gilson origin.

Flux problem case 2: GE03404G (“Unknown2”)

The IR of this spectrum shows small absorptions around 2916 and 2849 cm-1, but not enough to distinguish between the three mentioned flux types. But taking into account the significant different UV- VIS spectrum however, it is probably of a whole other origin we don’t have references of.

Flux problem case 3: GE03405G (“Unknown3”)

Showing a similar UV-VIS spectrum as Chatham and Lennix, and lacking absorption peaks around 2916 and 2849 cm-1, this spectrum probably is from one of these two origins.

c) Classification and dataset comparison

The flux minerals are easy to recognise, both in UV-VIS and IR,: in the blind classification, they were already grouped together in both UV-VIS (groups 2a-b-c, 5) and IR (group 7). A distinction has even been made between the presumed Gilson type (2c) on the one hand and the Chatham and Lennix types on the other hand (comprised in 2a-b). The spectrum of “Unknown2” origin has also been grouped apart. In classification 2, we grouped them all together based on the main role of the IR spectrum.

4.4.4. Additional features to distinguish synthetic from natural emeralds

In § 4.4.1, p. 53, we listed features described in literature that are typical for synthetic emeralds. We found however additional absorption peaks that we only saw in the latter. Where some natural emeralds show absorption around 3235 cm-1 (with sometimes a sprout to 3245 cm-1), a peak around 3220 cm-1 is only found in synthetic Lechleitner and emeralds from hydrothermal problem cases 1 & 2 (Figure 4.27). This is still different from an ammonium related peak at 3232 cm-1.

The peak/shoulder at 2443 cm-1 was present in all synthetic emeralds except for AGEE, and for problem case “Hy2”, but the latter showed as only type a maximum at 2450 cm-1. Some Colombian spectra may also show a band-like feature from 2445 cm-1 up to 2475 cm-1, but this has never been seen in their synthetic counterparts (Figure 4.27).

Figure 4.27. IR spectrum showing features to discrimate synthetic from natural emeralds. Below: orientating spectrum. Left: 3235 cm-1 (natural) vs. 3220 cm-1 (synthetic). Right: 2475 cm-1 (natural) vs. 2443 and 2450 cm-1 (synthetic)

4. 5. The question mark group of the studied emeralds

Dataset: 8 emeralds GE03600G GE03601G GE03602G GE03612G GE03613G GE03614G GE03615G GE08324G After our careful examination of the different emerald origins, it would be interesting to test if we could assign these 8 spectra to a certain provenance. The IR and UV-VIS characteristics are given in Table 7.2 in appendices and the spectra are depicted in Figure 4.28 and Figure 4.29. One spectrum, GE03601G, shows no clear IR spectrum: a lot of noise prohibits detailed examination.

Figure 4.28. IR spectra of the question mark group.

It is obvious from both UV-VIS and IR that all 8 emeralds are natural: the deep Fe2+ absorption around

-1 830 nm, the absence of rounded shoulders around a more or less triangular H2O peak around 5200 cm , and the absence of the 2443 and 2323 cm-1 peaks produce enough proof.

For GE03602G we could assign a Zimbabwean origin. In the IR spectrum, it has the typical triangular form, matching the 5500 – 5000 cm-1 region of Sandawana emeralds. Other matching features are the absences of the 2291 and 2340 cm-1 peaks. In the UV-VIS region, the strong transmission peak between 325-275 nm matches. However, this spectrum shows Fe3+ absorption around 372, not seen in our

65 reference samples. Another mismatch is the less sharp transmission bands. The position of the third transmission bands does also not fall between the range of the reference samples (705 vs. 725-750 nm). Other features we examined do match, but are not typical.

Figure 4.29. UV-VIS spectra of the question mark group.

GE08324G also lacks the 2291 cm-1 peak, excluding a Brazilian origin. The form of the 5200 cm-1 region, the normal UV transmission around 250-325 nm, low absorption in the 325-400 zone, the not complete absorption around 550-650 nm and the 705 nm maximum of the third transmission band point to Madagascar instead of a South-African or Zimbabwean origin.

Three other spectra we could assign a Madagascar or Indian origin: GE03612G, GE03613G, GE03614G. In the UV-VIS region, they show the band between 250-325 nm is the most intense of the range. They show strong absorption around the 325-400 nm peak. They also lack the 2291 cm-1 absorption band: we found Madagascar references showing the same feature. However, the 2340 cm-1 peak is not present, which is actually very distinct in Madagascar emeralds. An Indian origin is also possible, since UV-VIS spectrum matches except for the mentioned 250-325 nm zone. On the infrared region, we don’t have enough information on the Indian IR spectrum to conclude a match. The other origins differ too much.

Spectrum GE03615G is the only spectrum showing distinct absorption at 2291 cm-1. Its features all fit completely a Madagascar, Brazil, Zambian or South-African origins. The same counts for GE03600G, although the infrared spectrum does not say anything.

In GE03600G noise prohibits examination of the CO2 peak. The UV-VIS shows an intense UV transmission -1 at 250-325 nm. We also observe a wide H2O peak around 5200 cm . Features fit Brazilian, Zambian and Madagascar origins.

Conclusion: All spectra are natural and are not Colombian. But, except for GE03602G and GE08324G, we couldn’t make a clear spectroscopic based decision on the exact origin of these spectra. And even for these two, it is certainly not 100 % unambiguously, certainly not regarding the fact that we have no information on other origins.

4. 6. Treatments of emeralds

4.6.1. How to determine the presence of treatments in emeralds

The two most important – and most discussed – substances at this time are cedarwood oil and Opticon 224. Johnson (1999) stated already that the most common artificial resins (by which he primarily means Opticon 224) can, as pure substances, be distinguished from cedarwood oils by a combination of gemmological and spectroscopic techniques, but, other artificial resins cannot be so separated. This combination exists of the estimation of the filler’s refractive index (based on the presence or absence of a “flash effect”) followed by FT-IR and/or Raman analysis. Fillers show their presence mainly in the region between 3100 – 2800 cm-1. Johnson separated treatments in 4 groups based on their FT-IR spectroscopic features (Figure 4.30) and assigned with reasonable success a substance category (listed in Table 2.4, p. 8) to each group. In short: A contains only artificial resins, D only “presumed natural” essential oils, but in B and C this distinction is more problematic.

For Opticon treatment, peaks are at 2966, 2930 and 2872 cm-1. Cedarwood oil shows absorptions at 2955, 2928 and 2855 cm-1. However, slightly different values are possible, when comparing with research from HRD Antwerp and other sources (1999) sources. Armstrong et al. (2000) talk about a clear distinction in this range, but they did not make any further identification. We already mentioned in § 4.2.1, p. 31 that the presence of peaks in this region may be very ambiguous indeed. In addition, the coinciding presence of absorptions (2956, 2919, 2850 cm-1) due to external organic contamination (“filthy fingers”, Figure 4.6, p. 31) is another factor to take into account.

4.6.2. The information problem

HRD Antwerp’s dataset appeared very incomplete as regards info about treatments. It reports only 7 Opticon treatments, 1 with “coloured oil”, 1 is labelled “treated” and 30 ”not treated”. For 91 emeralds the possible presence of a filling is not yet investigated.

Table 4.13. List of the treated emeralds by the dataset, compared with our observations from classification 2.

Treatment According dataset According Class2 Treated Coloured oil Opticon Not treated ? No GE03543G GE03541G 30 spectra 31 spectra GE03540G GE9317G GE8989G Yes GE9321G GE9308G 60 spectra GE9322G Total 1 1 7 32 91

We examined the spectra of emeralds considered treated according the dataset (the spectra in the first three columns in Table 4.13), but we couldn’t find significant differences between the different types of treatments: only the relative intensities of the peaks may vary (Figure 4.31a). Certain absorptions also match peaks due to external organic contamination (as seen in Figure 4.6, p. 31). In two spectra, GE03543G and GE03541G, both considered treated according to the dataset, we found only the signs of these contamination peaks (Figure 4.31b). We are convinced that these two are indeed untreated samples. When we compare the spectra of Figure 4.31a with the treatment peaks mentioned in the previous paragraph, we see no clear match with neither Opticon or cedarwood oil.

A comparison with the rest of the emeralds we considered treated in Class2 lead to following conclusions. Emeralds from all natural origins showed a typical peak triplet or quadruplet, (quasi-)similar to the ones discussed above: exact positions of the four peaks may vary somewhat or the third small peak/shoulder at 2872 cm-1 may even be absent. Only in certain Zambian emeralds, two other types of absorption spectra were found (Figure 4.31c): “Zambian 1” comprises two26 spectra, “Zambian 2” three27 spectra. The other Zambian spectra showed the same spectra as in Figure 4.31a. Again, a match with cedarwood or Opticon is not clear, although they are not completely different.

26 GE03478G, GE03453G 27 GE03466G, GE03452G, GE03457G 68

Conclusion: although we are positive to trace the presence of treatments, we cannot further determine the type of treatment.

Figure 4.30. Representative FT-IR spectra of various Figure 4.31. Detail of representative IR spectra showing filling substances (Johnson et al., 1999). On the basis of the region that indicates the presence of a treatment. their spectra, Johnson et al. placed the substances in (a) Varying intensities of the peaks. (b) Two spectra we four infrared groups (A-D) and 17 subgroups (a-q). consider not treated. (c) Other, Zambian types of treatment (above: GE03478G, below: GE03452G).

4. 7. Discussion

4.7.1. Internal differences in emerald origins

Both UV-VIS and IR spectra of emeralds from the same provenance show significant varying features, as demonstrated. A first explanation would be that we have only discriminated on country level. Although this classification is valid for most countries, in which all deposits are formed under similar geological conditions, some countries contain emerald sources with significant different deposits. This counts for Brazilian deposits that have formed under two totally different conditions. This may explain the single Colombian-style infrared spectrum (footnote 6 on p. 44), or the Cr-free Brazilian emeralds Wood and Nassau (1968) discussed about (but as mentioned where not present in our set). No large-scale detailed research about the differences in the UV-VIS or IR spectrum of emeralds from different mines is around to our knowledge. In Madagascar, there are also two different deposits, the Mananjary and Ianapera deposits, containing emeralds with different compositions (§ 2.4.2.b). In India, the southern and northern deposits are also of totally different origin.

Deposits that occurred due to the same geological event also show spectral differences. The Zambian emeralds, all from the Kafubu area for example, are characterised by a high Fe3+ content, but as proved in the examined spectra, the accompanying UV-VIS feature is not always present. The same counts for the Sandawana emeralds, where the Fe2+ content seems to vary between low “quasi-Colombian” and high “Brazilian” amounts, as compared in Figure 4.9, p. 43. Also local variable conditions may thus have a large influence.

This is in contrary to emeralds in Colombia: Lebedev et al. (1983) compared spectra of the important Colombian mines and observed no remarkable differences in most mines (Figure 4.32). The Muzo, Chivor, and Cristo mines show the rounded shoulders around the 5273 cm-1 peak and the 2293 cm-1

-1 peak. The Coscuez mines however showed a more triangular form of the 5273 cm H2O peak, and a minor 2293 cm-1 peak. This is consistent with 2 of our 36 Colombian spectra (footnote 5 on p. 44) also showing these two features. Further details about these or other differences are unfortunately yet to be investigated.

Figure 4.32. IR spectra of emeralds from the different Colombian mines (Lebedev et al., 1983). 4.7.2. The value of spectroscopy for emerald origin determination purposes

For discrimination between natural and synthetic emeralds, we propose a first examination with a good quality UV-VIS spectroscopy, followed by further investigation by IR, if necessary. UV-VIS measurements are relatively cheap, quick, clear, and can directly distinguish four groups:

 The flux group is distinctive because of their lack of H2O related absorption bands in both the UV-VIS and IR region. o In IR, the Gilson type is distinctive from the Chatham and the Lennix type.  Another group has (almost) no Fe2+ associated feature in UV-VIS: these are the Colombian emeralds and chlorine bearing hydrothermal synthetics: the AAGE, Biron, Chinese, Linde- Regency and Malossi type. o These hydrothermal synthetics show in IR the chlorine related bands between 3000 and 2500 cm-1. These bands are only significantly different in the Malossi type. o The Linde-Regency type shows additional ammonium related bands at 3295 and 3232 cm-1. The AAGE, Biron and Chinese types are not significantly different.

 The third group shows distinct copper related bands in both UV-VIS and IR. The Russian type is distinctive from the Lechleitner and Tairus type because of its Fe3+ feature. Tairus may be further recognised by its lack of certain small Cr peaks.  The fourth group has a very distinct Fe2+ absorption band in UV-VIS. Further determination is not obvious, but certainly not imposible:

-1 o A typical small triangular shape of the 5500-5000 cm H2O peak points to a Zimbabwean IR spectrum. o However not conclusive, a Fe3+ absorption feature is indicative for a Zambian UV-VIS emerald spectrum. o A combination of less determining features may point to certain origins.

Other features in the IR spectrum are very useful to determine synthetic from natural emeralds. They are listed in Table 4.11 (p. 53) and § 4.4.4 (p. 64).

Although spectra from Colombian emeralds seem to be unique in natural emeralds by their low Fe2+ amount leading to the tabular form in the UV-VIS region and the typical H2O related features in the 5500- 5000 cm-1 region. Carefulness is required though, because these features are also typical in certain hydrothermal synthetic emeralds. Further, although we discussed emeralds from the most important origins, we should not forget other deposits: the typical H2O peak of Colombian emeralds is for example also reported in Norwegian emeralds (Rondeau, 2003). Still, the relatively easy detection of Colombian emeralds out of the examined natural and synthetic emerald spectra is very interesting, because they are the most sought-after and reach the highest market prices.

4.7.3. Polarised or non-polarised spectra for emeralds?

Would it be of additional value to use polarised spectra instead of non-polarised for UV-VIS and IR spectra, or at least take in mind the direction of the c-axis ? In order to obtain a quick technique to discriminate, we believe that the additionally gained parameters are not of extra significance. Quantitatively, the intensity of peaks/bands will vary anyway in some degree for different emeralds, and qualitatively, with our non-polarised spectra, we already discover all features.

4. 8. Further research

On this topic, our research is the first one on this scale, but still contains some hiatuses. Certain examined provenances do not contain enough species to draw solid conclusions (Indian, South-African,

Zimbabwean). Others are even not represented (e.g. Uralian, Australian, Austrian, Norwegian, Pakistan). Similar investigation on these provenances could bring more closure on the value of our used techniques. Additionally, a more detailed description on locality level might be interesting to determine the variations between emeralds from the same country or region.

Certain significant peaks we found in the infrared region are not yet assigned. Peaks at 3235-45, 2470- 72-75 cm-1 and the band between 4400-4000 cm-1 are well recognised, but a cause has not yet been described.

5. CONCLUSIONS

By applying UV-VIS and FT-IR spectroscopy on a set of 133 cut emeralds we evaluated if these techniques are valuable to distinguish synthetic from natural, to determine the geographic origin or synthetic type, and to identify treatments. This lead to fruitful results: (1) we recognised all synthetic emeralds, (2) assigned 78 % to the right origin/type and (3) are able to trace treatments.

A classification based on one or two reference specimens per region, lead to a correct assignment of 103 of the 132 emerald spectra (we ignored one trapiche emerald): we separated all the natural from the synthetic emeralds. We also correctly recognised all 16 flux-grown, all 14 hydrothermal synthetic and all 36 natural Colombian emeralds. The natural Zambian group also appeared distinctive, showing only 4 on 29 inconsistencies. The Brazilian and Indian emeralds comprised in fact a rest group containing also emeralds from Madagascar, Zimbabwe and South-Africa.

A good methodology would be to start with UV-VIS examination, followed by further discrimination with IR spectroscopy. The UV-VIS method is cheap, fast and easy and is able to clearly separate four groups:

(1) Synthetic flux emeralds are distinctive because of the lack of water related absorption bands in both UV-VIS and IR spectra. (2) The absence of Fe2+ absorptions is typical for natural Colombian and chlorine bearing hydrothermal synthetic types (AAGE, Biron, Chinese, Linde-Regency and Malossi). In IR, the chlorine related bands can unmistakably distinguish them. (3) Copper related hydrothermal synthetics show Cu2+ bands in both UV-VIS and IR. The Russian type is further distinctive by a Fe3+ absorption, the Cr-free Tairus type lacks certain chromium related peaks. (4) Other natural emeralds all show distinct Fe2+ absorption. In IR Zimbabwean emeralds also show unique water related features. Other UV-VIS and IR spectra are however too variable. An indication is a Fe3+ absorption peak that is mainly observed in Zambian emeralds. A combination of features may however suggest or exclude one or more origins.

The IR spectrum is very valuable to separate natural form synthetic emeralds. The presence of treatments is also revealed in this region showing absorption peaks between 3100 and 2800 cm-1. Further determination is unfortunately not obvious, because the numerous treatments show almost similar absorptions, mixtures are possible and contamination by external organic material shows absorptions in the same range.

Further research should focus on provenances/synthetic types we did not discuss or from which we had no (or not enough) specimens. For some countries where depositions formed under different geological conditions, additional discrimination on a more local scale is desired.

6. REFERENCES

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JOHNSON, M. L., ELEN, S. & MUHLMEISTER, S. 1999. On the Identification of Various Emerald Filling Substances. Gems & Gemology, 35 (2). 82-107. KAZMI, A. H. 1989. A brief overview of the geology and metallogenic provinces of Pakistan. In: KAZMI, A. J. & SNEE, L. W. (eds.), Emeralds of Pakistan – Geology, Gemology and Genesis. Geological Survey of Pakistan. New York, New York, U.S.A.: Geological Survey of Pakistan (Elite Publishers Limited, Karachi, Pakistan) and Van Nostrand Reinhold Company. 1–12. LAURS, B. M., SIMMONS, W. B., ROSSMAN, G. R., QUINN, E. P., MCCLURE, S. F., PERETTI, A., ARMBRUSTER, T., HAWTHORNE, F. C., FALSTER, A. U., GÜNTHER, D., COOPER, M. A. & GROBÉTY, B. 2003. Pezzottaite from Ambatovita, Madagascar: A New Gem Mineral. Gems & Gemology, 39 (4). 284-301. LEBEDEV, A. S., ILYIN, A. G. & KLYAKHIN, V. A. 1983. Variétés de beryl "gemme" hydrothermal. Revue de Gemmologie, 76 (4-5). MASHKOVTSEV, R. I. & SOLNTSEV, V. P. 2002. Channel constituents in synthetic beryl: ammonium Physics and Chemistry of Minerals, 29 (1). 65-71. MOINE, B., PENG, C. C. & MERCIER, A. 2004. Role of fluorine in the formation of the Mananjary emerald deposits (Eastern Madagascar). Comptes Rendus Geoscience, 336 (6). 513-522. NASSAU, K. 1983. The physics and chemistry of color : the fifteen causes of color (2nd Ed). New York: Wiley. 454. NASSAU, K. 1984. Gemstone enhancement : heat, irradiation, impregnation, dyeing, and other treatments which alter the appearance of gemstones, and the detection of such treatments (2nd Ed). London ; Boston: Butterworths. 221. NASSAU, K. & JACKSON, K. A. 1970. Trapiche Emeralds from Chivor and Muzo, Colombia. American Mineralogist, 55 (3-4). 416. O'DONOGHUE, M. 1997. Synthetic, imitation and treated gemstones (2nd Ed). Oxford: Butterworth- Heinemann. 203. OTTAWAY, T. L. 1991. The geochemistry of the Muzo emerald deposit, Colombia. MSc. Thesis, University of Toronto. OTTAWAY, T. L., WICKS, F. J., BRYNDZIA, L. T., KYSER, T. K. & SPOONER, E. T. C. 1994. Formation of the Muzo Hydrothermal Emerald Deposit in Colombia. Nature, 369 (6481). 552-554. PANJIKAR, J., RAMCHANDRAN, K. T. & K., B. 1997. New emerald deposits from southern India. Australian Gemmologist, 19 427-432. PAVIA, D. L., LAMPMAN, G. M., KRIZ, G. S. & VYVYAN, J. R. 2009. Introduction to Spectroscopy (4th Ed). Brooks/Cole. 656. PERKAMPUS, H. H. 1995. Encyclopedia of spectroscopy Ed). Weinheim ; Cambridge: VCH. PREINFALK, KOSTITSYN, Y. & MORTEANI, G. 2002. The pegmatites of the Nova Era-Itabira-Ferros pegmatite district and the emerald mineralisation of Capoeirana and Belmont (Minas Gerais, Brazil): geochemistry and Rb-Sr dating. Journal of South American Earth Sciences, 14 (8). 867- 887. RONDEAU, B. 2003. Les émeraudes vanadifères: approche des conditions de genèse par l'étude de deux gisements particuliers, Eidsvoll (Norvège) et La Pita (Colombie). Materiaux gemmes de reference

du museum national d’histoire naturelle: exemples de valorisation scientifique d’une collection de minéralogie et gemmologie. Nantes: IMN. 255. RUDNICK, R. L. & GAO, S. 2003. Composition of the Continental Crust. In: RUDNICK, R. L. (ed.) Treatise on Geochemistry, 3. 1-64. SCHMETZER, K. 1988. Characterization of Russian hydrothermally grown synthetic emeralds. Journal of Gemmology, 21 (3). 145-164. SCHMETZER, K., BERDESINSKI, W. & BANK, H. 1974. Über die Mineralart Beryll, ihre Farben und Absorptionsspectren. Zeitschrift der Deutschen Gemmologischen Gesellschaft, 23 (1). 5-39. SCHMETZER, K., KIEFERT, L., BERNHARDT, H. J. & BEILI, Z. 1997. Characterization of Chinese Hydrothermal Synthetic Emerald. Gems & Gemology, 33 (4). 276-291. SCHWARZ, D. 1994. Emeralds from the Mananjary Region, Madagascar: Internal Features Gems & Gemology, 30 (2). 88-101. SCHWARZ, D. & SCHMETZER, K. 2002. The definition of Emerald. Emeralds of the World., extraLapis 2 English. 74-78. SINKANKAS, J. 1981. Emerald and other beryls (2nd Ed). Radnor, Pa.: Chilton Book Co. 665. STERN, W. B. & HÄNNI, H. A. 1982. Energy-dispersive X-ray spectrometry: a non-destructive tool in gemmology. Journal of Gemmology, XVIII (285-296). STOCKTON, C. M. 1987. The Separation of Natural from Synthetic Emeralds by Infrared Spectroscopy. Gems & Gemology, 23 (2). 96-99. VAPNIK, Y., SABOT, B. & MOROZ, I. 2005. Fluid inclusions in Ianapera emerald, Southern Madagascar. International Geology Review, 47 (6). 647-662. WALTON, L. 2004. Exploration criteria for coloured gemstone deposits in the Yukon. Yukon Geological Survey, Open file 2004-10. 57-103. WILLARD, H. H., MERRITT, L. L. & DEAN, J. A. 1965. Instrumental methods of analysis (4th Ed). Princeton, N.J.: Van Nostrand. 784. WOOD, D. L. & NASSAU, K. 1968. Characterization of Beryl and Emerald by Visible and Infrared Absorption Spectroscopy. American Mineralogist, 53 (5-6). 777-800. YU, K. N., TANG, S. M. & TAY, T. S. 2000. PIXE studies of emeralds. X-Ray Spectrometry, 29 (4). 267-278. ZWAAN, J. C., KANIS, J. & PETSCH, E. J. 1997. Update on emeralds from the Sandawana Mines, Zimbabwe. Gems & Gemology, 33 (2). 80-100. ZWAAN, J. C., SEIFERT, A. V., VRÁNA, S., LAURS, B. M., ANCKAR, B., SIMMONS, W. B., FALSTER, A. U., LUSTENHOUWER, W. J., S., M., KOIVULA, J. I. & GARCIA-GUILLERMINET, H. 2005. Emeralds from the Kafubu Area, Zambia. Gems & Gemology, 41 (2). 116-148.

7. APPENDICES

Appendix 7. 1: List of all abbreviations and symbols used in tables

Appendix 7. 2: Details of UV-VIS and IR features of different known and unknown origins

iii

Table 7.1. UV-VIS features of all examined natural emerald origins and synthetic types...... iv

Table 7.2. IR features of all examined natural emerald origins and synthetic types...... v Table 7.3. UV-VIS and FT-IR features of the question mark group...... vi

Appendix 7. 3: Details of all samples: characteristics, classifications, treatments, details of UV-VIS and IR spectrum

vii

Table 7.4. All emerald samples, their characteristics, classifications and treatments……………….……….viii Table 7.5. UV-VIS features of all emerald samples…………………………………………………………………………………..xi Table 7.6. IR features of all emerald samples……………………………………………………………………………………….xiv

7. 1. List of all abbreviations and symbols used in tables

Abbr./symbol Explanation

Tr Transmission

Ab Absorption

B Band: broad absorption feature P Peak: sharp absorption feature S Shoulder: small kink in the spectrum

Bold border Characteristic feature Normal border Indicative feature

Bold and/or Example: +/-/0 underlined feature This feature state is mostly present + is mostly present. – and 0 are less present state

UV-VIS (nm) 250-325 highest Transmission between these wavelengths is highest of the whole spectra 0 Feature is absent - Feature is present, but only minor Based on the feature’s relation to other + Feature is present and distinctive features in the same spectra compared ++ Feature is very distinctive with the other spectra N/A It is not possible to make an observation Plateau Transmission band with no clear maximum 505-515 (510) The range of a feature in nm, with the most present value between brackets

IR (cm-1) 0 Feature is absent - Feature is present, but only minor + Feature is present and distinctive, without saturation ++ Feature is very distinctive, with signal saturation N/A Signal is too noisy or saturated to clearly observe a feature

7. 2. Details of UV-VIS and IR features of all known and unknown origins

Table 7.1. UV-VIS features of all examined natural emerald origins and synthetic types...... iv Table 7.2. IR features of all examined natural emerald origins and synthetic types...... v Table 7.3. UV-VIS and FT-IR features of the question mark group...... vi

iii

Table 7.1: UV-VIS features of all examined natural emerald origins (above) and synthetic types (below). UV-VIS feature (nm) Colombia Brazil Zambia India Madagascar Zimbabwe S-Africa

250-325 highest ? 0 0/+ +/0 0 +/0 0 0

Tr B1 325-400 ++ -/+/++ +/- 0 +/- +/- - 375-390 Max 1 350-370 375-390 (380) N/A 370-380 370-380 380 (385) Ab B1 400-450 ++ ++/+ ++ ++ ++ ++ ++

Min 1 420-430 425-430 430 N/A 430 430 430

Tr B2 475-525 ++ ++/+ ++/+ ++ ++ (sharp) ++ + 505-515 Max 2 505-510 505-515 (510) 515 505-510 510-515 510 (510) Ab B2 550-650 ++ ++ ++ + ++/+ ++ ++

Min 2 600-625 (610) 605-615 (610) 610-615 615 605-620 (610) 615 605

Tr B3 650-800 ++ ++/+ +/++ + ++/+ ++/+ ++

Max 3 735-775 (750) 705-730 710-730 705 700-720 (710) 725-750 (735) 715

Ab B3 800-875 - ++/+ +/++ + ++/+ +/- +

Min 3 N/A 840 840-850 840 830-850 (840) 840-860 (850) 830

Ab P1 370-372 0 0/++ ++/+/-/0 N/A 0/+ 0 0

Ab S 476-478 + 0/-/+ 0/- 0 0/-/+ 0 +

Ab S3 636 + + + + + + +

Ab S4 660 + 0/-/+ 0/-/+ + +/- + -

Ab Doublet 5 681 & 683/4 + ++ ++ ++ ++ ++ ++

Ab P6 957 ++ +/- + + +/- +/- - Tr B1-2-3 large Other remarks + sharp

Case 1 & 2 Case 3 UV-VIS feature (nm) Lechleitner AGEE Flux GE03544G Hy2 250-325 highest ? 0 0 0 0 0

Tr B1 325-400 ++ ++ + ++/+ ++/+

Max 1 355 355 350 375 345

Ab B1 400-450 ++ ++ ++ ++ ++

Min 1 430 430 430 430 430

Tr B2 475-525 ++ ++ + ++ ++

Max 2 505 505 505 505 505

Ab B2 550-650 ++ ++ ++ ++ ++

Min 2 600 600 605 600 605

Tr B3 650-800 - ++ ++ + ++

Max 3 660-675 780 730 710 760-785 (780)

Ab B3 800-875 ++ ++ - ++ 0

Min 3 750 750 plateau 750 N/A

Ab P1 370-372 0 0 0 ++ 0

Ab S 476-478 - - 0 + +/-/0

Ab S3 636 + + + + +

Ab S4 660 + + -/+ + -/0

Ab Doublet 5 681 & 683/4 ++ ++ + ++ ++

Ab P6 957 - + 0 + ++/+/-

Table 7.2. IR features of all examined natural emerald origins (above) and synthetic types (below). IR feature South- Colombia Brazil Zambia India Madagascar Zimbabwe Africa Ab P 6817 + + + + + +/-/ +

Additional left S 5600 0/+/- +/-/0 +/- + + ++ + Left S 5400 +/0 0/+ 0 0 0/- 0 0 Large P 5273 +/++ +/++ ++/+ ++ ++ + ++ Form P 5273 Extreme fine/mod. triangular/fine triangular wide triangular triangular triangular Right S 5100 +/-/0 0/+ 0 0 0 0 0 Form Right S 5100 round/0/dip 0/round 0 0 0 0 0

Small B 4400-4000 0/+/- 0/-/+ +/- + +/-/0 +/0 - Broad band 4000-3400 ++ ++ ++ ++ ++ ++ ++ Series of 5 6 distinct bands 0 0 0 0 0 0 0 3100-2300 Ab P 3235-45 + 0/+ 0/+ N/A +/0 +/0/ N/A 0 Ab Ps 3165 and 3115 +/-/0 0/+ 0 - +/-/0 0 + Ab zone 3000-2800 +/0 0/+ +/0 - 0/+ +/0 + Ab S 2475 +/-/0 0/+/2470-72 0/2470-72 0 0 0 0 Ab S 2443 0 0 0 0 0 0 0 Left CO2 S 2372 + + + + + + + Large CO2 P 2359 ++/+ ++/+ ++/+ N/A + + ++ Right CO2 S 2339 + + +/0 N/A +/++ 0/+ + Additional right CO2 S 2323 0 0 0 N/A 0 0 0 Ab P 2291 +/-/ -/0 + + N/A +/-/ -/0 0/- 0

Other remarks CO2 peaks = 2600-2400: Extreme mostly 1 large distinct H2O-CO2 abs. absorption bands

IR feature Case 1 Case 2 Lechleitner Agee Flux Case 3 Hy2 GE03544G GE03402G Ab P 6817 + + 0 +++ +++ +

Additional left S 5600 0 0 0 0 0 0

Left S 5400 + + 0 + + + Large P 5273 + + 0 + + + Form P 5273 fine fine 0 fine fine fine Right S 5100 + + 0 + + + Form Right S 5100 round round 0 round round round

Small B 4400-4000 0 0 0 0 0 0

Broad band 4000-3400 ++ ++ 0 ++ ++ ++

Series of 5 6 distinct bands 3100-2300 0 + 0 0 0 +

Ab P 3235-45 3220 0 0 0 3220 0

Ab Ps 3165 and 3115 + - 0 + + -

Ab zone 3000-2800 0 0 0 0 0 0 Ab S 2475 0 0 0 0 0 0

Ab S 2443 + 0 + + + 2450

Left CO2 S 2372 0 0 0 0 0 0 Large CO2 P 2359 0 0 0 - - 0

Right CO2 S 2339 0 0 0 0 0 0 Additional right CO2 S 2323 + + + + + +

Ab P 2291 0 0 0 0 0 0

Table 7.3. UV-VIS and FT-IR features of the question mark group.

Id GE03600G GE03601G GE03602G GE03615G GE08324G GE03612G GE03613G GE03614G UV-VIS Class 1 1a 1d 1b 1b 1a 1d 1d 1d IR Class 1 1 1 2 1 1 1 1 1 Class 2 code 2 2 2 2 2 3 3 3 Class 2 origine Bra Bra Bra Bra Bra India India India Class 2 Treated Yes Yes No Yes Yes Yes Yes Yes N - S N N N N N N N N UV-VIS 250-325 highest + 0 0 0 0 + + + Tr B1 325-400 - - + - - 0 0 0 Max 1 380 385 380 380 380 N/A N/A N/A Ab B1 400-450 ++ ++ ++ ++ ++ ++ ++ ++ Min 1 430 430 430 430 420 N/A N/A N/A Tr B2 475-525 ++ ++ ++ ++ ++ + + + Max 2 510 510 515 515 510 510 520 520 Ab B2 550-650 ++ ++ ++ ++ + + + + Min 2 615 615 615 610 610 615 610 610 Tr B3 650-800 ++ ++ + ++ ++ + + + Max 3 710 705 720 715 705 705 700 700 Ab B3 800-875 + ++ + + + + ++ ++ Min 3 830 830 840 830 830 840 840 840 Ab P 1 370-372 0 0 - 0 0 N/A N/A N/A Ab S 476-478 0 0 0 0 + 0 - 0 Ab S 3 636 + + + + + + + + Ab S 4 660 + - + - - + + + Ab Doublet 5 681 & 683/4 ++ ++ ++ ++ ++ ++ ++ ++ Ab P 6 957 + - - - + + + - FT-IR Ab P 6817 + + + + + + + + Aditional left S 5600 0 N/A + + + + + + Left S 5400 0 N/A 0 0 0 0 0 0 Large P 5273 ++ ++ + ++ ++ ++ ++ ++ Form P 5273 triangular wide triangular triangular triangular triangular triangular triangular Right S 5100 0 N/A 0 0 0 0 0 0 Form Right S 5100 0 N/A 0 0 0 0 0 0 Small B 4400-4000 + N/A 0 - - 0 0 0 Broad band 4000-3400 ++ ++ ++ ++ ++ ++ ++ ++ Series of 5 6 distinct bands 3100- 0 0 0 0 0 0 0 0 2300 Ab P 3235-45 N/A N/A + 0 0 0 0 0 Ab Ps 3165 and 3115 + N/A 0 3615 + 0 0 0 Ab zone 3000-2800 + + 0 + + + + - Ab S 2475 0 N/A 0 0 0 0 0 0 Ab S 2443 0 N/A 0 0 0 0 0 0 Left CO2 S 2372 + N/A + + + + + + Large CO2 P 2359 ++ N/A + ++ + + + + Right CO2 S 2339 + N/A 0 + + 0 0 0 Additional right CO2 S 2323 N/A N/A 0 0 0 0 0 0 Ab P 2291 N/A N/A 0 + + 0 0 0

7. 3. Details of all samples: characteristics, classifications, treatments, details of UV-VIS and IR spectrum

Table 7.4. All emerald samples, their characteristics, classifications and treatments……………………….viii Table 7.5. UV-VIS features of all emerald samples………………………………………………………………………………..xi Table 7.6. IR features of all emerald samples……………………………………………………………………………………….xiv

vii

Table 7.4. All emerald samples, their characteristics, classifications and treatments.

Id Stone Weight Shape UV VIS Class 1 IR Class 1 Class 2 code Class 2 origine Class 2 Treated Dataset Dataset origine - Match Dataset: Treatment? (ct) Nat/Syn type Class2? GE03376G EMERALD 0,404 Square Step 3d 5 6b Hy2 No S Hydroth. - AGEE NO Not treated GE03378G EMERALD 1,053 Rect.Step 3b 1 1 Col Yes N Colombia YES ? GE03379G EMERALD 1,628 Rect.Step 3b 2 1 Col No N Colombia YES ? GE03380G EMERALD 1,348 Rect.step 3b 1 1 Col Yes N Colombia YES ? GE03381G EMERALD 1,768 Rect.Step 3b 1 1 Col Yes N Colombia YES ? GE03382G EMERALD 1,063 Rect.Step 3a 1 1 Col Yes N Colombia YES ? GE03383G EMERALD 0,894 Rect.step 3b 1 1 Col Yes N Colombia YES ? GE03384G EMERALD 0,539 Rect.Step 3b 1 1 Col Yes N Colombia YES ? GE03385G EMERALD 0,398 Oval Cushion 1b 1 2 Bra Yes N Brazil YES ? GE03386G EMERALD 0,365 Oval Cushion 1b 2 2 Bra No N Brazil YES ? GE03387G EMERALD 0,394 Oval Cushion 1c 2 4 Zam No N Brazil NO ? GE03388G EMERALD 0,355 Oval Cushion 1a 2 2 Bra No N Brazil YES ? GE03389G EMERALD 0,393 Oval Cushion 1a 2 2 Bra No N Brazil YES ? GE03390G EMERALD 0,330 Oval Cushion 1b 2 2 Bra No N Brazil YES ? GE03391G EMERALD 0,422 Oval Cushion 1a 2 2 Bra No N Brazil YES ? GE03394G EMERALD 1,195 Oval Cushion 1a 1 2 Bra Yes N Brazil YES ? GE03395G EMERALD 0,933 Oval Cushion 1a 1 2 Bra Yes N Brazil YES ? GE03396G EMERALD 1,384 Oval Cushion 1c 1 4 Zam Yes N Brazil NO ? GE03397G EMERALD 1,207 Oval Cushion 1c 1 4 Zam Yes N Brazil NO ? GE03398G EMERALD 1,455 Oval Cushion 1a 2 2 Bra No N Brazil YES ? GE03399G EMERALD 1,006 Oval Cushion 1b 2 2 Bra Yes N Brazil YES ? GE03400G EMERALD 1,505 Rect.Step 2c 6 5a Flux No S Flux YES Not treated GE03401G EMERALD 1,453 Rect.Step 2c 6 5a Flux No S Flux YES Not treated GE03402G EMERALD 1,003 Square Step 6 8 6a Hy1 No S Flux NO Not treated GE03404G EMERALD 0,695 Rect.Step 5 6 5b Flux No S Flux YES Not treated GE03405G EMERALD 0,206 Round 2b 6 5a Flux No S Flux YES Not treated GE03406G EMERALD 0,198 Round 2a 6 5a Flux No S Flux YES Not treated GE03407G EMERALD 1,375 Rect. Step 2b 6 5a Flux No S Flux - Chatham YES Not treated GE03408G EMERALD 1,607 Rect.Step 2b 6 5a Flux No S Flux - Chatham YES Not treated GE03409G EMERALD 2,371 Oval Cushion 2a 6 5a Flux No S Flux - Chatham YES Not treated GE03410G EMERALD 0,933 Rect.step 2b 6 5a Flux No S Flux - Chatham YES Not treated GE03411G EMERALD 0,762 Rect.step 2a 6 5a Flux No S Flux - Chatham YES Not treated GE03412G EMERALD 0,926 Rect.step 2a 6 5a Flux No S Flux - Chatham YES Not treated GE03413G EMERALD 1,034 Rect.step 2b 6 5a Flux No S Flux - Chatham YES Not treated GE03414G EMERALD 0,730 Oval Cushion 2a 6 5a Flux No S Flux - Chatham YES Not treated GE03415G EMERALD 1,123 Oval Cushion 2b 6 5a Flux No S Flux - Chatham YES Not treated GE03416G EMERALD 0,998 Pear Cushion 2a 6 5a Flux No S Flux - Chatham YES Not treated GE03417G EMERALD 0,959 Oval Cushion 1a 2 2 Bra No N Madagascar NO ? GE03418G EMERALD 1,034 Oval Cushion 1a 1 2 Bra Yes N Madagascar NO ? GE03419G EMERALD 0,890 Oval Cushion 1a 2 2 Bra No N Madagascar NO ? GE03420G EMERALD 0,626 Oval Cushion 1b 2 2 Bra No N Madagascar NO ? GE03421G EMERALD 0,798 Oval Cushion 1b 2 2 Bra No N Madagascar NO ? GE03422G EMERALD 0,846 Oval Cushion 1c 2 2 Bra No N Madagascar NO ? GE03423G EMERALD 0,748 Oval Cushion 1b 1 2 Bra Yes N Madagascar NO ? GE03424G EMERALD 0,832 Oval Cushion 1b 2 2 Bra No N Madagascar NO ? GE03425G EMERALD 0,948 Oval Cushion 1a 2 2 Bra No N Madagascar NO ? GE03428G EMERALD 2,567 Rect.Step 3c 1 1 Col Yes N Colombia YES ? viii

Id Stone Weight Shape UV VIS Class 1 IR Class 1 Class 2 code Class 2 origine Class 2 Treated Dataset Dataset origine - Match Dataset: Treatment? (ct) Nat/Syn type Class2? GE03429G EMERALD 1,810 Oval Cushion 3c 1 1 Col Yes N Colombia YES ? GE03430G EMERALD 1,024 Oval Cushion 3a 2 1 Col No N Colombia YES ? GE03431G EMERALD 1,422 Oval Cushion 3a 2 1 Col No N Colombia YES ? GE03432G EMERALD 1,668 Oval Cushion 3a 2 1 Col Yes N Colombia YES ? GE03433G EMERALD 1,859 Oval Cushion 3a 2 1 Col No N Colombia YES ? GE03434G EMERALD 0,860 Oval Cushion 3c 1 1 Col Yes N Colombia YES ? GE03435G EMERALD 1,456 Rect.Step 3c 1 1 Col Yes N Colombia YES ? GE03436G EMERALD 1,331 Oval Cushion 3c 1 1 Col Yes N Colombia YES ? GE03437G EMERALD 0,597 Rect Cushion 3b 1 1 Col Yes N Colombia YES ? GE03438G EMERALD 0,950 Oval Cushion 3c 1 1 Col Yes N Colombia YES ? GE03439G EMERALD 0,853 Oval Cushion 3a 1 1 Col Yes N Colombia YES ? GE03440G EMERALD 0,958 Rect.Step 3c 2 1 Col No N Colombia YES ? GE03443G EMERALD 1,297 Oval Cushion 3a 1 1 Col Yes N Colombia YES ? GE03444G EMERALD 0,679 Oval Cushion 3a 1 1 Col Yes N Colombia YES ? GE03445G EMERALD 1,970 Oval Cushion 3c 2 1 Col No N Colombia YES ? GE03446G EMERALD 0,926 Oval Cushion 3c 1 1 Col Yes N Colombia YES ? GE03447G EMERALD 0,546 Pear Cushion 3c 1 1 Col Yes N Colombia YES ? GE03449G EMERALD 0,553 Oval Cushion 3a 2 1 Col No N Colombia YES ? GE03450G EMERALD 1,016 Rect.Step 3a 1 1 Col Yes N Colombia YES ? GE03451G EMERALD 0,564 Oval Cushion 3a 1 1 Col Yes N Colombia YES ? GE03452G EMERALD 0,660 Oval Cushion 1c 3 4 Zam Yes N Zambia YES ? GE03453G EMERALD 0,895 Oval Cushion 1c 3 4 Zam Yes N Zambia YES ? GE03454G EMERALD 0,660 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03455G EMERALD 0,650 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03456G EMERALD 0,750 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03457G EMERALD 0,806 Oval Cushion 1c 3 4 Zam Yes N Zambia YES ? GE03458G EMERALD 0,736 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03459G EMERALD 0,735 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03460G EMERALD 0,758 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03461G EMERALD 0,911 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03462G EMERALD 0,736 Oval Cushion 1a 2 2 Bra No N Zambia NO ? GE03463G EMERALD 0,780 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03464G EMERALD 0,850 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03465G EMERALD 0,816 Oval Cushion 1c 1 4 Zam No N Zambia YES ? GE03466G EMERALD 0,728 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03467G EMERALD 0,694 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03468G EMERALD 0,940 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03469G EMERALD 0,906 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03470G EMERALD 0,673 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03471G EMERALD 0,736 Oval Cushion 1c 2 4 Zam No N Zambia YES ? GE03472G EMERALD 0,850 Oval Cushion 1c 2 4 Zam No N Zambia YES ? GE03473G EMERALD 0,710 Oval Cushion 1c 2 4 Zam No N Zambia YES ? GE03474G EMERALD 0,830 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03475G EMERALD 0,750 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03476G EMERALD 1,056 Oval Cushion 1c 2 4 Zam No N Zambia YES ? GE03477G EMERALD 0,820 Oval Cushion 1c 1 4 Zam Yes N Zambia YES ? GE03478G EMERALD 0,767 Oval Cushion 1c 3 4 Zam Yes N Zambia YES ? GE03540G EMERALD 1,409 Rect.Cushion 3a 1 1 Col Yes N Colombia YES Coloured oil GE03541G EMERALD 1,377 Rect. Cushion 3a 2 1 Col No N Colombia YES Opticon GE03542G EMERALD 1,604 ROUND 3d 5 6b Hy2 No S Hydrothermal YES Not treated GE03543G EMERALD 2,158 SQUARE 3d 5 6b Hy2 No S Hydrothermal YES Treated GE03544G EMERALD 1,573 Rect. Cushion 1c 4 6a Hy1 No S Hydrothermal YES Not treated

Id Stone Weight Shape UV VIS Class 1 IR Class 1 Class 2 code Class 2 origine Class 2 Treated Dataset Dataset origine - Match Dataset: Treatment? (ct) Nat/Syn type Class2? GE03545G EMERALD 2,189 SQUARE 3a 5 6b Hy2 No S Hydrothermal YES Not treated GE03546G EMERALD 1,682 ROUND 3d 5 6b Hy2 No S Hydrothermal YES Not treated GE03547G EMERALD 1,159 Rect. Cushion 3d 5 6b Hy2 No S Hydrothermal YES Not treated GE03548G EMERALD 1,238 Rect. Cushion 3d 5 6b Hy2 No S Hydrothermal YES Not treated GE03550G EMERALD 1,395 Rect. Cushion 3a 5 6b Hy2 No S Hydrothermal YES Not treated GE03551G EMERALD 1,268 Rect. Cushion 3d 5 6b Hy2 No S Hydrothermal YES Not treated GE03552G EMERALD 1,309 Rect. Cushion 3d 5 6b Hy2 No S Hydrothermal YES Not treated GE03600G EMERALD - - 1a 1 2 Bra Yes N ? NO ? GE03601G EMERALD - - 1d 1 2 Bra Yes N ? NO ? GE03602G EMERALD - - 1b 2 2 Bra No N ? NO ? GE03612G EMERALD 1,192 Rect. 1d 1 3 India Yes N ? NO ? GE03613G EMERALD 1,156 Sq. cabochon 1d 1 3 India Yes N ? NO ? GE03614G EMERALD 0,622 Sq. cabochon 1d 1 3 India Yes N ? NO ? GE03615G EMERALD - - 1b 1 2 Bra Yes N ? NO ? GE03635G EMERALD - - 1b 1 2 Bra Yes N Sandawana NO ? GE03636G EMERALD - - 1b 7 3 India Yes N Sandawana NO ? GE03637G EMERALD - - 3b 2 3 India No N Sandawana NO ? GE03638G EMERALD - - 1b 2 3 India No N Sandawana NO ? GE03639G EMERALD - - 1b 7 3 India No N Sandawana NO ? GE03640G EMERALD - - 1d 1 3 India Yes N Sandawana NO ? GE08324G EMERALD - - 1a 1 2 Bra Yes N ? YES ? GE8330G EMERALD 0,630 Rect. step 7 2 6a Hy1 No S Hydroth. - YES Not treated Lechleitner GE8608G EMERALD 0,318 Pear 2a 6 5a Flux No S Flux - Lennix YES Not treated GE8609G EMERALD 0,602 Rect. step 7 4 6a Hy1 No S Hydroth. - YES Not treated Lechleitner GE8986G EMERALD 1,959 Round 1b 1 3 India No N India YES Not treated GE8989G EMERALD 0,879 Pear 3c 1 2 Bra Yes N South Africa NO Not treated GE9308G EMERALD 0,653 Round 3c 1 2 Bra Yes N Brazil YES Not treated GE9317G EMERALD 0,133 Round 3a 1 1 Col Yes N Colombia YES Opticon GE9321G EMERALD 0,141 Round 3a 1 1 Col Yes N Colombia YES Opticon GE9322G EMERALD 0,125 Round 3a 1 1 Col Yes N Colombia YES Opticon GE9323G EMERALD 0,093 Round 3a 1 1 Col Yes N Colombia YES Opticon GE9324G EMERALD 0,120 Round 3c 1 1 Col Yes N Colombia YES Opticon GE9326G EMERALD 0,100 Round 3a 1 1 Col Yes N Colombia YES Opticon GE9901G TRAPICHE 1,915 Exagonal 8 2 N Colombia - Not treated EMERALD cabochon

Table 7.5. UV-VIS features of all emerald samples.

Ab P 1 370 1 Ab P

Dataset origine origine Dataset

Ab B1 400 Ab B1 550 Ab B2 800 Ab B3

Tr B1 325 Tr B2 475 Tr B3 650 Tr

Ab S 476 Ab S 5 Ab Doublet

681 & 683/4 681 &

Ab P 6 957 6 Ab P

Ab S 3 636 3Ab S 660 4Ab S

250

highest

Ma 2 Max 3 Max

Min 1 Min 2 Min 3

type

------

400 450 525 650 800 875 372 478

325

x 1 x

GE03376G Hydroth. - AGEE 0 + 345 ++ 430 ++ 505 ++ 605 ++ 780 0 N/A 0 - + - ++ ++ GE03378G Colombia 0 ++ 357 ++ 430 ++ 505 ++ 605 ++ 740 - N/A 0 - + + + ++ GE03379G Colombia 0 ++ 357 ++ 430 ++ 505 ++ 610 ++ 740 - N/A 0 + + + + ++ GE03380G Colombia 0 ++ 357 ++ 430 ++ 505 ++ 605 ++ 740 - N/A 0 + + + + ++ GE03381G Colombia 0 ++ 357 ++ 430 ++ 505 ++ 615 ++ 740 - N/A 0 + + + + ++ GE03382G Colombia 0 ++ 357 ++ 430 ++ 505 ++ 605 ++ 740 - N/A 0 + + + + ++ GE03383G Colombia 0 ++ 357 ++ 430 ++ 505 ++ 605 ++ 740 - N/A 0 - + + + ++ GE03384G Colombia 0 ++ 368 ++ 420 ++ 505 ++ 610 ++ 735 - N/A 0 - - + + ++ GE03385G Brazil 0 + 380 ++ 430 ++ 510 ++ 615 ++ 720 + 840 0 + + + ++ + GE03386G Brazil 0 + 380 ++ 430 ++ 510 ++ 610 ++ 720 + 840 0 0 + + ++ + GE03387G Brazil + ++ 385 + 430 ++ 505 ++ 615 + 725 + 840 ++ - + + ++ + GE03388G Brazil 0 + 380 ++ 430 ++ 510 ++ 610 ++ 705 ++ 840 0 0 + + ++ + GE03389G Brazil 0 - 390 ++ 430 ++ 510 ++ 610 + 705 ++ 840 0 - + + ++ - GE03390G Brazil 0 - 380 ++ 430 ++ 510 ++ 610 + 710 ++ 840 0 - + + ++ - GE03391G Brazil 0 + 380 ++ 430 ++ 510 ++ 610 + 705 ++ 840 0 0 + + ++ - GE03394G Brazil 0 + 380 ++ 430 ++ 510 ++ 610 ++ 705 ++ 840 0 + + + ++ + GE03395G Brazil 0 + 385 ++ 430 ++ 515 ++ 605 ++ 710 ++ 840 0 + + + ++ + GE03396G Brazil + + 385 ++ 430 ++ 510 ++ 610 + 725 + 840 ++ + + 0 ++ + GE03397G Brazil + + 385 ++ 430 ++ 510 ++ 610 + 725 + 840 ++ 0 + - ++ + GE03398G Brazil 0 + 385 ++ 425 ++ 510 ++ 610 ++ 710 ++ 840 0 + + + ++ + GE03399G Brazil 0 + 375 ++ 430 ++ 510 ++ 610 ++ 715 ++ 840 0 + + + ++ + GE03400G Flux 0 + 350 ++ 430 + 505 ++ 605 ++ 730 0 N/A 0 0 + -/+ + 0 GE03401G Flux 0 + 350 ++ 430 + 505 ++ 605 ++ 730 0 N/A 0 0 + -/+ + 0 GE03402G Flux + N/A (372 abs) N/A (372 abs) ++ 430 ++ 505 ++ N/A 0 N/A ++ N/A ++ 0 0 0 0 0 GE03404G Flux 0 0 N/A ++ N/A + 530 - 605 ++ 740 0 N/A 0 0 0 0 0 0 GE03405G Flux 0 + 350 ++ 430 + 505 ++ 605 ++ 730 - plateau 0 0 + -/+ + 0 GE03406G Flux 0 + 350 ++ 430 + 505 ++ 605 ++ 730 - plateau 0 0 + -/+ + 0 GE03407G Flux - Chatham 0 + 350 ++ 430 + 505 ++ 605 ++ 730 - plateau 0 0 + -/+ + 0 GE03408G Flux - Chatham 0 + 350 ++ 430 + 505 ++ 605 ++ 730 - plateau 0 0 + -/+ + 0 GE03409G Flux - Chatham 0 + 350 ++ 430 + 505 ++ 605 ++ 730 - plateau 0 0 + -/+ + 0 GE03410G Flux - Chatham 0 + 350 ++ 430 + 505 ++ 605 ++ 730 - plateau 0 0 + -/+ + 0 GE03411G Flux - Chatham 0 + 350 ++ 430 + 505 ++ 605 ++ 730 - plateau 0 0 + -/+ + 0 GE03412G Flux - Chatham 0 + 350 ++ 430 + 505 ++ 605 ++ 730 - plateau 0 0 + -/+ + 0 GE03413G Flux - Chatham 0 + 350 ++ 430 + 505 ++ 605 ++ 730 - plateau 0 0 + -/+ + 0 GE03414G Flux - Chatham 0 + 350 ++ 430 + 505 ++ 605 ++ 730 - plateau 0 0 + -/+ + 0 GE03415G Flux - Chatham 0 + 350 ++ 430 + 505 ++ 605 ++ 730 - plateau 0 0 + -/+ + 0 GE03416G Flux - Chatham 0 + 350 ++ 430 + 505 ++ 605 ++ 730 - plateau 0 0 + -/+ + 0 GE03417G Madagascar + + 380 ++ 430 ++ 510 ++ 610 ++ 700 ++ 840 0 + + + ++ - GE03418G Madagascar 0 + 380 ++ 430 ++ 510 ++ 610 ++ 700 ++ 840 0 + + - ++ - GE03419G Madagascar 0 + 380 ++ 430 ++ 510 ++ 610 ++ 710 ++ 840 0 + + + ++ + GE03420G Madagascar 0 + 370 ++ 430 ++ 510 ++ 610 ++ 710 ++ 840 0 - + + ++ + GE03421G Madagascar 0 - 380 ++ 430 ++ 510 ++ 615 ++ 720 + 840 0 0 + + ++ + GE03422G Madagascar 0 + 380 ++ 430 ++ 505 ++ 610 + 710 ++ 840 + - + + ++ - GE03423G Madagascar 0 + 380 ++ 430 ++ 510 ++ 620 ++ 720 + 850 0 + + + ++ -

Ab P 1 Ab 370

Ab B1 400 Ab B2 550 Ab B3 800 Ab

Dataset

Tr B1 Tr325 B1 Tr475 B2 Tr650 B3

Ab S 476 S Ab

Ab Doublet 5 Doublet Ab

681 683/4 &

Ab P 6 Ab 957

Ab S 3 S 636 Ab 4 S 660 Ab

250

highest

origine origine

Max 1 Max 2 Max 3 Max

- 1 Min 2 Min 3 Min

- - - -

type -

450 650 875

400 525 800 372 478

325

GE03424G Madagascar 0 + 380 ++ 430 ++ 510 ++ 615 ++ 715 ++ 840 0 - + + ++ - GE03425G Madagascar 0 +/- 380 ++ 430 ++ 510 + 605 ++ 700 ++ 830 0 + + + ++ - GE03428G Colombia 0 + 350 ++ 425 ++ 505 ++ 605 ++ 740 - N/A 0 + + + - ++ GE03429G Colombia 0 + 357 ++ 430 ++ 505 + 610 ++ 750 - N/A 0 0 0 + 0 ++ GE03430G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 625 ++ 740 - N/A 0 + + + + ++ GE03431G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 610 ++ 740 - N/A 0 + + + + ++ GE03432G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 620 ++ 750 - N/A 0 0 - + + ++ GE03433G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 600 ++ 740 - N/A 0 + + + + + GE03434G Colombia 0 - 350 ++ 430 ++ 525 ++ 605 ++ 750 - N/A 0 - + + + ++ GE03435G Colombia 0 - 350 ++ 430 ++ 505 ++ 620 ++ 750 - N/A 0 - + + + ++ GE03436G Colombia 0 + 350 ++ 430 ++ 505 ++ 610 ++ 750 - N/A 0 - + + + ++ GE03437G Colombia 0 + 370 ++ 430 ++ 505 ++ 620 ++ 740 - N/A 0 - + + + ++ GE03438G Colombia 0 - 350 ++ 430 ++ 520 ++ 610 ++ 760 - N/A 0 + - 0 - ++ GE03439G Colombia 0 + 350 ++ 430 ++ 505 ++ 620 ++ 760 - N/A 0 0 - 0 - + GE03440G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 610 ++ 775 - N/A 0 0 0 0 680 ++ GE03443G Colombia 0 + 350 ++ 430 ++ 505 ++ 610 ++ 750 - N/A 0 0 + + + ++ GE03444G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 610 ++ 750 - N/A 0 - + + + ++ GE03445G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 600 ++ 750 - N/A 0 + + 0 + ++ GE03446G Colombia 0 - 350 ++ 430 ++ 510 ++ 610 ++ 775 - N/A 0 + + + + ++ GE03447G Colombia 0 - 350 ++ 430 ++ 510 ++ 610 ++ 750 - N/A 0 + + + + ++ GE03449G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 620 ++ 750 - N/A 0 + + + ++ ++ GE03450G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 620 ++ 750 - N/A 0 + + + + ++ GE03451G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 610 ++ 740 - N/A 0 + + + + ++ GE03452G Zambia + + 385 ++ 430 ++ 510 ++ 610 ++ 725 + 840 ++ - + - ++ + GE03453G Zambia + + 385 ++ 430 ++ 510 ++ 610 + 715 ++ 840 ++ 0 + 0 ++ + GE03454G Zambia + + 385 ++ 430 ++ 510 ++ 610 ++ 725 + 840 ++ 0 + 0 ++ + GE03455G Zambia + + 385 ++ 430 + 510 ++ 610 + 730 + 840 ++ 0 + 0 ++ + GE03456G Zambia + + 385 ++ 430 + 510 ++ 610 + 730 + 840 + 0 + 0 ++ + GE03457G Zambia + + 385 ++ 430 + 510 ++ 610 + 730 + 840 + 0 + 0 ++ + GE03458G Zambia + + 385 ++ 430 + 510 ++ 610 + 730 + 840 ++ 0 + 0 ++ + GE03459G Zambia + + 385 ++ 430 + 510 ++ 610 + 730 + 840 + 0 + 0 ++ + GE03460G Zambia + + 385 ++ 430 + 510 ++ 610 + 730 + 840 + 0 + 0 ++ + GE03461G Zambia + + 385 ++ 430 + 510 ++ 610 + 730 - 850 ++ - + 0 ++ + GE03462G Zambia 0 +/- 380 ++ 430 ++ 510 ++ 610 + 710 ++ 840 0 - + + ++ - GE03463G Zambia + + 385 ++ 430 + 510 ++ 610 + 725 + 840 ++ 0 + 0 ++ + GE03464G Zambia + + 385 ++ 430 + 510 ++ 610 + 730 + 840 ++ - + 0 ++ + GE03465G Zambia + + 385 ++ 430 ++ 510 ++ 610 ++ 725 + 840 ++ 0 + + ++ + GE03466G Zambia + + 385 ++ 430 + 510 ++ 610 + 730 + 840 ++ - + 0 ++ + GE03467G Zambia + + 380 ++ 430 ++ 510 ++ 610 + 720 + 840 ++ 0 + 0 ++ + GE03468G Zambia + + 390 ++ 430 ++ 510 ++ 610 + 720 + 840 ++ 0 + 0 ++ + GE03469G Zambia + + 375 ++ 430 ++ 515 ++ 615 ++ 730 + 840 0 0 + - ++ + GE03470G Zambia + + 385 ++ 430 ++ 505 ++ 615 + 720 + 840 ++ 0 + 0 ++ + GE03471G Zambia + + 380 ++ 430 ++ 510 ++ 615 + 730 + 840 + - + - ++ + GE03472G Zambia + - 385 ++ 430 ++ 510 ++ 615 + 725 + 840 - - + + ++ + GE03473G Zambia + - 385 ++ 430 + 510 ++ 605 + 725 + 840 - 0 + + ++ - GE03474G Zambia + + 380 ++ 430 ++ 510 ++ 610 + 730 + 840 ++ 0 + 0 ++ +

xii

Ab P 1 Ab 370

Ab B1 400 Ab B2 550 Ab B3 800 Ab

Dataset origine origine Dataset

Tr B1 Tr325 B1 Tr475 B2 Tr650 B3

Ab S 476 S Ab

Ab Doublet 5 Doublet Ab

681 683/4 &

Ab P 6 Ab 957

Ab S 3 S 636 Ab 4 S 660 Ab

250

highest

Max 1 Max 2 Max 3 Max

- 1 Min 2 Min 3 Min

- - - -

type -

450 650 875

400 525 800 372 478

325

GE03475G Zambia + + 380 ++ 430 ++ 510 ++ 610 + 730 + 840 ++ 0 + 0 ++ + GE03476G Zambia + + 385 ++ 430 ++ 505 ++ 615 + 720 + 840 ++ - + - ++ + GE03477G Zambia + + 380 ++ 430 ++ 510 ++ 610 + 730 + 840 ++ 0 + 0 ++ + GE03478G Zambia + + 380 ++ 430 ++ 510 ++ 610 + 730 + 840 ++ - + 0 ++ + GE03540G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 620 ++ 740 - N/A 0 + - + + ++ GE03541G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 620 ++ 750 - N/A 0 - - + + ++ GE03542G Hydrothermal 0 ++ 345 ++ 430 ++ 505 ++ 605 ++ 780 0 N/A 0 + + 0 ++ + GE03543G Hydrothermal 0 ++ 345 ++ 430 ++ 505 ++ 605 ++ 780 0 N/A 0 + + - ++ ++ GE03544G Hydrothermal 0 N/A (372 abs) N/A (372 abs) ++ 430 ++ 505 ++ 605 + 710 0 N/A ++ 0 + + ++ ++ GE03545G Hydrothermal 0 ++ 345 ++ 430 ++ 505 ++ 605 ++ 770 0 N/A 0 + + - ++ ++ GE03546G Hydrothermal 0 ++ 345 ++ 430 ++ 505 ++ 605 ++ 765 0 N/A 0 - + - ++ ++ GE03547G Hydrothermal 0 ++ 345 ++ 430 ++ 505 ++ 605 ++ 780 0 N/A 0 + + 0 ++ - GE03548G Hydrothermal 0 ++ 345 ++ 430 ++ 505 ++ 605 ++ 780 0 N/A 0 + + - ++ ++ GE03550G Hydrothermal 0 + 345 ++ 430 ++ 505 ++ 605 ++ 760 0 N/A 0 0 + 0 ++ ++ GE03551G Hydrothermal 0 ++ 345 ++ 430 ++ 505 ++ 605 ++ 785 0 N/A 0 0 + - ++ ++ GE03552G Hydrothermal 0 ++ 345 ++ 430 ++ 505 ++ 605 ++ 785 0 N/A 0 + + 0 ++ ++ GE03600G ? + - 380 ++ 430 ++ 510 ++ 615 ++ 710 + 830 0 0 + + ++ + GE03601G ? 0 - 385 ++ 430 ++ 510 ++ 615 ++ 705 ++ 830 0 0 + - ++ - GE03602G ? 0 + 380 ++ 430 ++ 515 ++ 615 + 720 + 840 - 0 + + ++ - GE03612G ? + 0 N/A ++ N/A + 510 + 615 + 705 + 840 N/A 0 + + ++ + GE03613G ? + 0 N/A ++ N/A + 520 + 610 + 700 ++ 840 N/A - + + ++ + GE03614G ? + 0 N/A ++ N/A + 520 + 610 + 700 ++ 840 N/A 0 + + ++ - GE03615G ? 0 - 380 ++ 430 ++ 515 ++ 610 ++ 715 + 830 0 0 + - ++ - GE03635G Sandawana 0 + 380 ++ 430 ++ 510 ++ 615 + 725 + 840 0 0 + + ++ - GE03636G Sandawana 0 ++ 370 ++ 430 ++ 515 ++ 615 ++ 735 +/- 840 0 0 + + ++ + GE03637G Sandawana + ++ 370 ++ 430 ++ 515 ++ 615 ++ 735 +/- 850 0 0 + + ++ - GE03638G Sandawana 0 ++ 370 ++ 430 ++ 515 ++ 615 ++ 750 - N/A 0 0 + + ++ + GE03639G Sandawana + ++ 370 ++ 430 ++ 515 ++ 615 ++ 725 + 850 0 0 + + ++ + GE03640G Sandawana 0 ++ 370 ++ 430 ++ 515 ++ 615 ++ 735 +/- 860 0 0 + + ++ + GE08324G ? 0 - 380 ++ 420 ++ 510 + 610 ++ 705 + 830 0 + + - ++ + Hydroth. - GE8330G + ++ 355 ++ 430 ++ 505 ++ 605 - 680 0 N/A 0 + + + ++ ++ Lechleitner GE8608G Flux - Lennix 0 + 350 ++ 430 + 505 ++ 605 ++ 730 - plateau 0 0 + -/+ + 0 Hydroth. - GE8609G 0 ++ 355 ++ 430 ++ 505 ++ 606 - 660 0 N/A 0 + + + ++ - Lechleitner GE8986G India 0 0 N/A ++ N/A ++ 515 + 615 + 705 + 840 N/A 0 + + ++ + GE8989G South Africa 0 - 380 ++ 430 ++ 510 ++ 605 ++ 715 + 830 0 + + - ++ - GE9308G Brazil + - 380 ++ 430 ++ 515 ++ 610 ++ 730 +/- 840 0 + + - ++ + GE9317G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 610 ++ 760 - N/A 0 + + + + ++ GE9321G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 610 ++ 750 - N/A 0 + + + + ++ GE9322G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 610 ++ 750 - N/A 0 + + + + ++ GE9323G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 610 ++ 760 - N/A 0 + + + + ++ GE9324G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 620 ++ 760 - N/A 0 0 + + + ++ GE9326G Colombia 0 ++ 350 ++ 430 ++ 505 ++ 615 ++ 750 - N/A 0 + + + + ++ GE9901G Colombia 0 ++ 394 - 430 ++ 505 - 615 + 680 ++ 840 + 0 + 0 + +

xiii

Table 7.6. IR features of all emerald samples

Left CO2 S 2372 Left CO2

Dataset origine origine Dataset and 3165 Ab Ps

Ab zone 3000 Ab zone

Additional left left Additional

distinct bands bands distinct

Small B 4400 B Small

Ab P 3235 Ab P

Large P 5273 Large

Form Right S Right Form 6 5 Series of

Form P 5273 Form

Large CO2 P Large

Right S 5100 SRight

Broad band Broad

Right CO2 S CO2 Right

right CO2 S CO2 right

Left S 5400 Left S

4000 3100

Additional Additional

Ab P 6817 Ab P 2291 Ab P

Ab S 2475 Ab S 2443 Ab S

S 5600

- -

5100 4000 3400 2300 3115 2800 2359 2339 2323

type

- -

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xvi

8. ABSTRACT (DUTCH)

IR EN UV-VIS SPECTROSCOPIE VAN SMARAGD EDELSTENEN, EEN INSTRUMENT OM NATUURLIJKE EDELSTENEN TE

ONDERSCHEIDEN VAN SYNTHETISCHE EN/OF BEHANDELDE?

Inleiding en onderzoeksmethode

Smaragd behoort tot een van de vier meest waardevolle edelstenen ter wereld. Het is de groene berilvariëteit dat zijn kleur dankt aan substituties van aluminium door chroom en, in mindere mate, vanadium. Omwille van diens hoge en afkomstafhankelijke verkoopwaarde is gedetailleerd onderzoek naar het bepalen van geografische oorsprong van groot belang.

Tot nu toe bestaat er echter nog geen feilloze methode om op een niet-destructieve manier alle herkomsten te achterhalen. Om deze reden zullen we twee spectroscopische technieken testen op hun waarde om (1) synthetische van natuurlijke smaragden te onderscheiden, (2) verschillende oorsprongsgebieden of synthetische types te herkennen en (3) opvullingmiddelen te ontdekken en te determineren. Deze vullingmiddelen worden veelal toegepast omdat beril erg fragiel is. Niet alle middelen worden echter aanvaard, omwille van hun synthetisch en/of kleurend karakter.

In dit kader werd een set van 133 geslepen smaragden uit de collectie van HRD Antwerp spectroscopisch onderzocht. De eerste spectroscopische techniek maakt gebruik van het ultraviolet en zichtbaar licht (UV-VIS), de tweede omvat Fourier-Transform spectroscopie in het infrarode (FT-IR) gedeelte van het spectrum. Onze strategie bestaat er uit om classificaties te maken aan de hand van eigen observaties. Een eerste, “blinde” groepering voor UV-VIS en IR afzonderlijk moet, zonder enige voorkennis, al duidelijk maken waar de trends liggen en wat de knelpunten zijn. Nadien zullen we aan de hand van enkele referentiespecimens van verscheidene oorsprongen bekijken wat significante verschillen kunnen zijn en de stalen opnieuw classificeren, dit keer aan de hand van de twee technieken samen. Vervolgens vergelijken we onze classificaties met de informatie uit de dataset van HRD Antwerp.

In de dataset zitten natuurlijke smaragden van Brazilië, Colombia, India, Madagaskar, Zambia, Zimbabwe en Zuid-Afrika. Op de laatste na behoren deze landen ook tot de grootste smaragdindustrieën van de wereld, met Colombia op kop. Smaragden van Colombia worden gezien als de meest waardevolle en ze zijn ook uniek omdat ze als enige gevormd zijn in een milieu van zwarte schalies en pekelstromen. Andere afzettingen zijn geassocieerd met pegmatietintrusies in (ultra)mafische gesteenten of worden gevormd onder invloed van fluïda van metamorfe oorsprong.

De synthetische smaragden bestaan uit twee grote groepen. Enerzijds zijn er de flux smaragden, waarbij hier belangrijk is dat ze zonder aanwezigheid van water onder lagere drukken en temperaturen gevormd worden. Anderzijds zijn er de hydrothermaal gevormde smaragden, die meer het natuurlijk proces (met hogere drukken en temperaturen) benaderen. Op elk techniek bestaan er ook nog meerdere variaties.

Resultaten

In Figuur 8.1 staan een typisch UV-VIS en IR spectrum. Bij elke absorptie staan ook de teweegbrengende factoren.

Figuur 8.1. Boven: voorbeeld van een UV-VIS spectrum. Onder: voorbeeld van een IR spectrum.

De resultaten van de classificaties onderlijnen het potentieel van de gebruikte onderzoekstechnieken en dataverwerking. Na vergelijking met de dataset bleken we voor 103 van de 132 (78 %) onderzochte mineralen een juiste oorsprong te hebben toegekend (1 trapiche smaragd werd buiten beschouwing gelaten wegens zijn duidelijke herkomst). Meer bepaald, we hebben (1) alle synthetische van de natuurlijke smaragden onderscheiden, (2) 74 van de 102 natuurlijke smaragden naar hun juiste origine verwezen, (3) alle 15 synthetische flux smaragden en alle 14 hydrothermale synthetische smaragden

“ontdekt”. Van de natuurlijke mineralen hebben we alle 36 Colombiaanse smaragden kunnen onderscheiden en vertoonde de smaragden van Zambia slechts 4 inconsistenties.

Voor beide spectroscopische technieken bezitten Colombiaanse smaragden karakteristieken die bijna uniek zijn ten opzichte van stenen van andere natuurlijke afkomst. Als de technieken samen gebruikt worden is er zelfs geen twijfel mogelijk. De meest uitgesproken eigenschappen zijn (1) zeer lichte Fe2+ absorptie in hun UV-VIS spectra (enkele Zimbabwaanse vertoonden ook een zwakke Fe2+ absorptie) en (2) een fijne piek op 5273 cm-1 omgeven door twee ronde schouders in het IR spectrum (cf. Figuur 8.1), waar andere natuurlijke smaragden eerder één brede driehoekige piek vertonen (op één Braziliaans spectrum na).

Smaragden van Zambia hebben als richtend kenmerk een uitgesproken Fe3+ piek in hun UV-VIS spectrum; dit is echter geen unieke eigenschap, bewijzen ook enkele smaragden van Brazilië en Madagaskar. Zimbabwaanse smaragden vertonen een zeer typische kleine, maar uitgesproken driehoekvormige piek rond 5273 cm-1, niet waargenomen bij andere oorsprongen. Voor de andere natuurlijke smaragden vonden we geen duidelijke karakteristieken, ook al kan een combinatie van geselecteerde eigenschappen toch op een bepaalde origine wijzen.

Belangrijker – en duidelijker – is het onderscheid tussen natuurlijke en synthetische smaragden:

 Synthetische flux smaragden zijn relatief eenvoudig te onderscheiden wegens hun kenmerkende afwezigheid van watergerelateerde absorptiebanden, zowel in hun UV-VIS als in hun IR spectra. o We onderzochten Chatham, Lennix en Gilson flux types. De eerste twee vertonen gelijkaardige karakteristieken, maar het Gilson type kan nog verder onderscheiden worden aan de hand van kleine IR piekjes en een licht verschillend UV-VIS spectrum.  Russische, Lechleitner en Tairus type hydrothermale smaragden vertonen kopergerelateerde absorptie rond 750 nm in UV-VIS. Dit zien we in geen enkele natuurlijke smaragd. Ook het IR geeft dit weer door een verhoogde absorptie rond de 7000 cm-1. Het Russische type vertoont hierbij ook nog eens een sterke Fe3+ absorptieband rond 370 nm in het UV-VIS spectrum. Bij het op vanadium gebaseerde Tairus type ontbreken enkele Cr gerelateerde piekjes.  AAGE, Biron, Chinese, Linde-Regency en Malossi hydrothermale types hebben een UV-VIS spectrum dat sterk lijkt op dat van een natuurlijke Colombiaanse, met als enige (klein) verschil dat ze nog minder Fe2+ absorptie vertonen. Hun IR spectrum vertoont daarentegen tussen 3000 en 2500 cm-1 een serie duidelijke absorptiepieken en banden te wijten aan chloor.  Andere kenmerken die hydrothermaal synthetisch gevormde smaragden typeren zijn :

III

o De zone rond de 5273 cm-1 piek is zoals Colombiaanse natuurlijke smaragden fijn met geronde schouders.

-1 o Absorpties in de zone rond 2200-2350 cm (te wijten aan CO2) zijn afwezig of minimaal. Ze vertonen wel een schouder rond 2320 cm-1 waar natuurlijke smaragden er een hebben rond 2340 cm-1. o Verder vonden we soms nog een schouder op 2443 cm-1 en een absorptiepiek op 3220 cm-1 die we beiden in geen enkel natuurlijke smaragd terugvonden.

Behandelingen van smaragden laten sporen na tussen 3100 en 2800 cm-1 in het infrarood spectrum. Dit resulteert in drie of vier duidelijke absorptiepiekjes; deze zijn ook te zien in Figuur 8.1. Een verder onderscheid is echter amper met spectroscopische middelen te maken. Dit komt omdat er heel veel types op de markt zijn die resulteren in gelijkaardige absorptiepieken, mengvormen geregeld voorkomen en absorptiestructuren te wijten aan extern organisch vuil dat aan de rand van de smaragden durft blijven plakken de piekjes gedeeltelijk kunnen overlappen.

Discussiepunten en verder onderzoek

De vraag of een indeling van natuurlijke smaragdtypes in landen wel gerechtvaardigd is dringt zich op. Voor de meeste landen wel, aangezien ze slechts één fase van smaragdvorming gekend hebben. In andere landen zoals Brazilië, India, en Madagaskar verschillen de afzettingen wel. Dit zou al een gedeelte van de interne variaties in zowel UV-VIS als IR spectra kunnen verklaren. Nochtans bewijzen variaties in spectra uit landen zoals Zimbabwe en Zambia, die slechts één fase van smaragdvorming kennen, dat ook op regionaal/lokaal niveau verschillen in geologische condities een grote rol spelen. Een aantal belangrijke smaragdbronnen, zoals Rusland, Pakistan en Afghanistan werden niet in ons onderzoek opgenomen. Deze opgenoemde topics zijn prima voer voor verder onderzoek.

Conclusies

We stellen een methodiek voor beginnend met een eerste onderzoek met UV-VIS spectroscopie: deze methode is immers snel, gemakkelijk en kan al de belangrijkste zaken vaststellen. Nadien kan indien nodig nog verder onderscheid gemaakt worden met IR spectroscopie. Hiermee kan men (1) natuurlijke van synthetische smaragden onderscheiden, (2) Colombiaanse en Zimbabwaanse natuurlijke smaragden herkennen of een onderscheid maken tussen flux synthetische en koper- en chloorhoudende hydrothermaal synthetische smaragden, en (3) vaststellen of de onderzochte smaragd een behandeling heeft ondergaan.