Agates from Kerrouchen (The Atlas Mountains, Morocco): Textural Types and Their Gemmological Characteristics

Article Agates from Kerrouchen (The Atlas Mountains, Morocco): Textural Types and Their Gemmological Characteristics

Lucyna Natkaniec-Nowak 1, Magdalena Duma ´nska-Słowik 1,*, Jaroslav Pršek 1, Marek Lankosz 2, Paweł Wróbel 2, Adam Gaweł 1, Joanna Kowalczyk 1 and Jacek Kocemba 1

1 Faculty of Geology, Geophysics and Environmental Protection, Department of Mineralogy, Petrography and Geochemistry, AGH University of Science and Technology, 30 Mickiewicza av., 30-059 Kraków, Poland; [email protected] (L.N.-N.); [email protected] (J.P.); [email protected] (A.G.); [email protected] (J.K.); [email protected] (J.K.) 2 Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, 30 Mickiewicza av., 30-059 Kraków, Poland; [email protected] (M.L.); pawel.wrobel@ﬁs.agh.edu.pl (P.W.) * Correspondence: [email protected]

Academic Editor: Raymond M. Coveney, Jr. Received: 30 April 2016; Accepted: 7 July 2016; Published: 26 July 2016

Abstract: Agate nodules from Kerrouchen (Khénifra Province, Meknés-Tafilalet Region) in Morocco occur in Triassic basalts and reach up to 30 cm in diameter. Monocentric, banded agates—mainly in pastel pink, grey, white and yellow—with infiltration canals (osculum) are observed. Raman microspectroscopy revealed that the agates mainly consist of low quartz and subordinately moganite with distinctive 460 and 501 cm´1 marker bands, respectively. Linear mapping indicated that moganite mainly concentrates in grey zones of the monocentric agate nodules. The other types, polycentric and pseudostalactitic agates, are usually brown and red and contain minerals such as hematite and goethite. They form both regular and irregular mosaics rich in ornamentation. Occasionally, aggregates of copper sulphides or titanium oxides (rutile) can also be observed. These minerals are sometimes accompanied by carbonaceous material marked by 1320 and 1585 cm´1 Raman bands. It seems that formation of agates from Kerrouchen was induced by Si-rich and Fe-moderate fluids. Copper sulphides, rutile, and carbonates (possibly calcite) were most likely incorporated during post-magmatic processes. The origin of solid bitumen can be the result of hydrothermal or hypergenic processes.

Keywords: agate; Kerrouchen; Morocco; colour pigments; microtexture

1. Introduction The crystallization of agates worldwide has proceeded for millions of years. The oldest gems were found in Pilbara rock formations (3500–2700 Ma) and the youngest originated from volcanic tuffs from the Yucca Mt. in the USA (13 Ma) [1]. The genesis of agates is strictly connected with volcanic and hypergenic solutions, which are the source of various ions and organic matter. The most common origin of agates is a complex, multi-stage silica crystallization from these solutions with changing chemical composition [2] or cyclic crystallization of pigments from the silica gel in the pores of volcanic rocks [3]. Generally, formation of agates takes place in volcanic rocks, hydrothermal veins, or in sediments. In basic volcanic rocks they crystallize in vesicles of former gas or ﬂuid bubbles. In contrast, agate genesis in acidic volcanic host rocks starts with the formation of lithophysae (high-temperature crystallization domains). Agates form in holes of these lithophysae, which are the result of tensional stress and/or degassing and crystallization in the cooling melt [4]. As a result, agate

Minerals 2016, 6, 77; doi:10.3390/min6030077 www.mdpi.com/journal/minerals Minerals 2016, 6, 77 2 of 13 occurs in different forms—usually they are the same as the original pores in the host rocks, but may undergo pseudomorphosis after different primary minerals such as calcite or barite. The central part of the geode is very often filled with different cryptocrystalline quartz varieties—amethyst, smoky quartz, prasiolite, rock crystals, or morion. Agate nodules can reach diameters from several centimetres up to several tenths of centimetres, and can reach weights of up to several hundreds of kilograms. During the last decades, agates from Morocco have become interesting gems among mineral collectors. Agates occur in the Triassic basalts at many localities in the High Atlas–Sidi Rahal [3–5], Asni, Tizi-n-Tichka area, Agouim, Ahouli, and Kerrouchen [6–9]. The agates from each locality have unique characteristics, such as type and colour, as well as the general pattern revealed on its polished section. All of them can reach up to 30 cm in diameter. Sidi Rahal and Asni agates have greyish-white, bluish-white, or red to brown colours, whereas agates from Kerrouchen show a diversity of colours in the individual zones from the white to grey, yellow, orange, blue, red, and even brown in one sample. The agate geodes from Kerrouchen are also unique by their variety of patterns and morphological structures. They are mainly monocentric, subordinately polycentric to pseudostalactitic. Monocentric banded agates or horizontally stratified agates are rarities. Agates with stalactites similar to the so-called “plume” agates from Texas (USA) are the most sought-after in that country. The other popular forms of agates are white agates—Cacholong (“kalmuck agate”) with blue-grey or pinkish chalcedony zones—or agates with “Wagler effect” (i.e., three-dimensional chatoyant effect), which can be also found in the Kerrouchen area [6]. The first geological descriptions of agates from the Atlas Mountains were made in the 1940s (vide [6–8]). However, the “agate fever” did not start there until of the 20th century. However, such interest in Moroccan agates by collectors worldwide has not resulted in the increased amounts of the scientific publications. Recent articles mainly contain descriptions of agates’ localities in the High Atlas Mountains, with focus placed on general geology of the region or on the exploration of these ornamental stones for jewellery (e.g., [5,6,8–13]). A more complex mineralogical study of agates from Sidi Rahal was conducted by Dumańska-Słowiket al. [3]. This study described, in detail, the internal texture of the agates as well as number and character of solid inclusions found in them. In the present study, continuing the research on Moroccan agates, the distribution of different silica phases in rhythmically zoned agates from Kerrouchen, together with the characteristic of solid inclusions occurring in their coloured zones, are presented. To ascertain the agates’ formation, we have applied optical transmission microscopy, scanning electron-microscopic observations (SEM-EDS) supported by Raman microspectroscopy (RS), and X-ray fluorescence analysis (XRF).

2. Geological Setting Morocco is situated in a western part of the folded Atlas Mountains, which cover an area of more than 2000 km long from the Atlantic coastline to Kabiska Bay in the Mediterranean area. These mountains are the elongations of the European Alpine orogenic system. The Atlas Unit was formed, folded, and dislocated at the beginning of Paleogene. It consists of two main folded units: the internal with Middle, High Atlas, Sahara Atlas, and Anti-Atlas [14], and the external with Tell Atlas and Rif [15]. These units are divided by Morocco Meset (200–1500 m a.s.l.) and Shott Plane (750–1000 m a.s.l.). The High Atlas is built by Paleozoic rocks—crystalline schists, quartzites, limestones, and Hercynian volcanic rocks. The upper parts are covered by huge layers of folded Jurassic and Cretaceous limestones with Lower Paleogen limestones and sandstones. The areas richest in agates are: Tizi-n-Tichka, Asni and Sidi Rahal [6]. The agate deposit in Kerrouchen was found at the beginning of this century. This small village is situated in the Khénifra Province (Middle Morocco) and is surrounded by the High Atlas to the south, Rif Mountains to the north, and Wadi Muluja valley to the east (Figure1). The agates can be collected on the mountain slopes, in the agricultural ﬁelds, as well as along the road running from Bouma to Kerrouchen. They are found within the Triassic and Lower Jurassic volcanic rocks–basalts, whose outcrop in the area in the form of a crescent 10 ˆ 20 km in size. Minerals 2016, 6, 77 3 of 13 Minerals 2016, 6, 77 3 of 13

FigureFigure 1. Simplified 1. Simplified geological geological map map ofof thethe Kerrouchen area, area, modified modified after after Arboleya Arboleya et al. et [16]. al. [16]. Legend:Legend: Miocen Miocen and and Quaternary: Quaternary: different different sediments—alluvialsediments—alluvial sands, sands, gravels gravels and and clays; clays; Cretaceous: Cretaceous: conglomerates, flysch, detritic facies; Jurassic: different limestones; Triassic: different types of conglomerates, flysch, detritic facies; Jurassic: different limestones; Triassic: different types of limestones, basaltic volcanics with agates; Permian: acidic volcanics; Devonian: detritic facies; limestones, basaltic volcanics with agates; Permian: acidic volcanics; Devonian: detritic facies; Ordovician: different shales; Cambrian: limestones and detritic facies. Ordovician: different shales; Cambrian: limestones and detritic facies. 3. Experimental Section 3. Experimental Section Agate samples representing all three morphological types were selected for the investigation. AgateThey were samples examined representing with binoculars all three in order morphological to select the proper types material were selected for the research for the investigation.using the TheySEM-EDS, were examined RS, and with XRF binocularsmethods. in order to select the proper material for the research using the SEM-EDS, RS, and XRF methods. 3.1. Microscopic Analyses 3.1. MicroscopicThin sections Analyses of all agate samples were examined with an Olympus BX 51 polarizing microscope (Olympus, Tokyo, Japan) with a magnification range from 40× to 400×. Backscattered Thin sections of all agate samples were examined with an Olympus BX 51 polarizing microscope electron (BSE) observations were performed on polished sections using an FEI Quanta 200 field ˆ ˆ (Olympus,emission Tokyo, gun scanning Japan) withelectron a magnificationmicroscope equi rangepped fromwith energy-dispersive 40 to 400 . Backscattered spectroscopy (FEI, electron (BSE)Hillsboro, observations OR, USA). were performedThe system was on polished operated sectionsat 20 kV accelerating using an FEI voltage Quanta in low-vacuum 200 field emission mode. gun scanningScanning electron electron microscope microscopy equipped provided with informat energy-dispersiveion on the distribution spectroscopy and quantity (FEI, Hillsboro, of solid OR, USA).inclusions The system found was operatedin agates at 20and kV acceleratingtheir genera voltagel chemical in low-vacuum composition. mode. Combined Scanning with electron microscopyRaman providedspectroscopy, information it enables on identification the distribution of all andmineral quantity and organic of solid phases inclusions found found within in an agates and theiragate’s general matrix. chemical composition. Combined with Raman spectroscopy, it enables identification of all mineral and organic phases found within an agate’s matrix. 3.2. Raman Spectroscopy 3.2. RamanRaman Spectroscopy spectra of silica phases and the most pronounced solid inclusions were recorded using a Thermo Scientific DXR Raman microscope (Thermo Fisher, Waltham, MA, USA), equipped with Raman spectra of silica phases and the most pronounced solid inclusions were recorded using 100-, 50- and 10× magnification objectives, operating in a confocal mode and working in the a Thermo Scientific DXR Raman microscope (Thermo Fisher, Waltham, MA, USA), equipped with 100-, backscatter geometry. The polished sample pieces were excited with a 532 nm high-power laser. The 50- andlaser 10 focusˆ magnification diameter was objectives,1–2 μm. operating in a confocal mode and working in the backscatter geometry. The polished sample pieces were excited with a 532 nm high-power laser. The laser focus diameter was 1–2 µm. µ In the line-mapping experiments, 320 spectra with 50 m steps were obtained for two monocentric and polycentric agates polished pieces. The most intensive bands for quartz (460 cm´1) and moganite (501 cm´1) in each point of the analytical grid were recorded. Minerals 2016, 6, 77 4 of 13

3.3. X-Ray Fluorescence Two-dimensional maps of elemental distribution were done with a laboratory micro-XRF setup. The setup utilizes a low-power X-ray tube with a Mo-target and silicon drift X-ray detector. Primary radiation from the X-ray tube is focused with a polycapillary lens—the nominal spot size is 16.4 µm full width at half maximum (FWHM). Detailed information about the setup can be found elsewhere [17]. The measurements were performed in standard 45˝/45˝ geometry, where the angles between impinging beam, sample normal, and detector axis equalled 45˝. The X-ray tube voltage and current were 50 kV and 1 mA, respectively. The sample surface was placed out of focus of the primary radiation beam, in order to achieve effective size of a beam of approximately 200 µm FWHM. The 300 µm slices of samples were mounted between two 2.5 µm thick Mylar films stretched across a plastic holder. The holder was placed on a motorized stage that allows sample positioning with micrometre resolution. For the mapping of monocentric and polycentric agates the step size (pixel size), equal to 200 µm in the horizontal and vertical directions, was used. The first map consists of 104 ˆ 141 pixels, equal to 20.8 ˆ 28.2 mm2. The second map was 139 ˆ 136 pixels, or 27.8 ˆ 27.2 mm2. The sample acquisition times were 2.5 s per pixel and 3 s per pixel, respectively. The net intensities of the characteristic lines were calculated by nonlinear least-squares fitting with AXIL-QXAS software package. Correlations of Fe vs. Mn, Mn vs. Ti, Fe vs. Ti, and Cu vs. Mn were calculated only for analytical points measured inside the agate samples.

4. Results The agates from Kerrouchen show a rich diversity of colours and morphological features. They range in size from 12 to 30 cm in diameter, and differ in internal structure, thickness of individual zones, colours, as well as patterns. Generally, they can be divided into three groups: monocentric, polycentric, and pseudostalactitic (Figure2). Generally, the monocentric agates are white-grey. They very rarely exhibit the inﬁltrative channel (osculum) (Figure2A). Their external, very thin zones are likely composed of chalcedony, while the centre with thick layers could be built of ﬁne individual quartz or chalcedony (Figure2A,B). Locally, some monocentric agates contain additional red-brownish zones at the rim, which result from the scattered compounds of iron within a silica matrix (Figure2G,H). The polycentric (multi-eye) agates show a distinctive spotted appearance (Figure2D). The spots contain red-pinkish concentric bands which are reminiscent of numerous “eyes” at the grey-brown silica background. The pseudostalactite agates are characterized by a random, irregular arrangement of individual layers which resemble stalactite-like forms existing on the top or bottom of the rock (Figure2C,I). They are generally coloured red, brown, and white. An aperture is located in the central part of most of these agates (Figure2E,F,I). Minerals 2016, 6, 77 5 of 13 Minerals 2016, 6, 77 5 of 13

FigureFigure 2. 2.Kerrouchen Kerrouchen agates: (A (A) )monocentric monocentric agate agate with with osculum, osculum, 3.5 × 3.55.5 ˆ× 2.95.5 cm,ˆ 2.9greyish cm, white greyish whiteinternal internal and andreddish reddish to dark-brown to dark-brown external external zone; ( zone;B) monocentric (B) monocentric agate, 3.2 agate, × 4.1 3.2× 2.1ˆ cm,4.1 greyishˆ 2.1 cm, greyishwhite whiteto pinkish to pinkish internal internal and reddish and reddish to dark-brown to dark-brown external external zone; (C zone;) pseudostalactie (C) pseudostalactie agate, 3.2 agate, × 5.8 × 1.1 cm, light-brown, reddish, orange to greyish-white interior and light-brown external zone; 3.2 ˆ 5.8 ˆ 1.1 cm, light-brown, reddish, orange to greyish-white interior and light-brown external (D) polycentric agate, 6.1 × 4.5 × 1.5 cm, pink, red to orange interior and light-brown external zone; zone; (D) polycentric agate, 6.1 ˆ 4.5 ˆ 1.5 cm, pink, red to orange interior and light-brown external (E) pseudostalactite agate, 3.4 × 4.4 × 0.9 cm, orange, red, brown to greyish-white interior and zone; (E) pseudostalactite agate, 3.4 ˆ 4.4 ˆ 0.9 cm, orange, red, brown to greyish-white interior light-brown external zone; (F) pseudostalactite agate, 2.9 × 6.6 × 1.3 cm, orange, red, brown to and light-brown external zone; (F) pseudostalactite agate, 2.9 ˆ 6.6 ˆ 1.3 cm, orange, red, brown greyish-white interior and light-brown external zone; (G) monocentric agate, 3.5 × 6.0 × 1.3 cm, to greyish-white interior and light-brown external zone; (G) monocentric agate, 3.5 ˆ 6.0 ˆ 1.3 cm, light-brown, orange to greyish-white interior and dark-brown external zone; (H) monocentric agate, light-brown, orange to greyish-white interior and dark-brown external zone; (H) monocentric agate, 4.0 × 4.3 × 1.1 cm, light-brown to greyish-white interior and dark-brown to red external zone; 4.0 ˆ 4.3 ˆ 1.1 cm, light-brown to greyish-white interior and dark-brown to red external zone; (I) pseudostalactite agate, 6.2 × 11.5 × 0.5 cm, light-brown, orange to greyish-white interior and ˆ ˆ (I)light-brown pseudostalactite external agate, zone. 6.2 11.5 0.5 cm, light-brown, orange to greyish-white interior and light-brown external zone. 4.1. Microscopic Observations 4.1. Microscopic Observations In monocentric and polycentric agates, the zones of different generations of silica are easily observedIn monocentric (Figure 3A,B,E,F). and polycentric The external agates, parts the of ag zonesate nodules, of different at the generationscontact with the of silicahost rock, are easilyare observedusually (Figurecomposed3A,B,E,F). of fibrous The and external crypto-crystalline parts of agate chalcedony, nodules, which at the locally contact form with the thesequence host rock, of areminor usually laminas composed interleaving of fibrous each and other. crypto-crystalline The boundaries chalcedony, between the which zones locally are sharp. form the In sequencethe inner of minorparts laminas of the interleavingnodules the each youngest other. Thegeneration boundaries of silica between (perfectly the zones formed are sharp. quartz) In thecrystallized. inner parts of theSometimes nodules it the is accompanied youngest generation by opaque of silicaminerals (perfectly and/or formedorganic quartz)matter (Figure crystallized. 3A,B,E,F). Sometimes Locally, it is accompaniedthe infiltrative by channel opaque can minerals be observed and/or in the organic agates. matter (Figure3A,B,E,F). Locally, the infiltrative channelThe can presence be observed of colouring in the agates. compounds (iron oxides and/or hydroxides, carbonaceous matter) is variableThe presence in the agates. of colouring However, compounds they mainly (iron occur oxides in polycentric and/or hydroxides, and pseudostalactite carbonaceous varieties, matter) whereas monocentric agates are significantly depleted of them. Generally, these pigments form is variable in the agates. However, they mainly occur in polycentric and pseudostalactite varieties, randomly dispersed aggregates within fine-crystalline and spherulitic chalcedony (Figure 3C,D) or whereas monocentric agates are significantly depleted of them. Generally, these pigments form are concentrated along with the borders between the individual layers. In some agates’ nodules, randomly dispersed aggregates within fine-crystalline and spherulitic chalcedony (Figure3C,D) or Fe-compounds cluster around spherulitic chalcedony grains (Figure 3E,F) forming characteristic are concentrated along with the borders between the individual layers. In some agates’ nodules, concentric rings (“eyes”). In pseudostalactitic agates a mixture of Fe-compounds and organic matter Fe-compoundsconcentrates in cluster the stalacti aroundtic-like spherulitic forms (Figure chalcedony 3G,H). grains (Figure3E,F) forming characteristic concentric rings (“eyes”). In pseudostalactitic agates a mixture of Fe-compounds and organic matter concentrates in the stalactitic-like forms (Figure3G,H).

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FigureFigure 3.3.Images Images ofof microtexturesmicrotextures inin variousvarious agateagate typestypes fromfrom Kerrouchen,Kerrouchen, observedobserved inin transmittedtransmitted andand polarizedpolarized light;light; 1N1N andand NX:NX: monocentricmonocentric ( A(A,B,B);), pseudostalactic pseudostalactic ( C(C,D,D,G,G,H,H);), polycentric polycentric ( E(E,F,F).).

Agates’Agates’ pigmentspigments can can be be observed observed under under SEM. SEM. They They form beautifulform beautiful regular regular and irregular and irregular mosaics richmosaics in ornamentation rich in ornamentation (Figure4 B,C).(Figure Their 4B,C). frequency Their frequency of occurrence of occurrence is variable is variable and differs and differs from samplefrom sample to sample. to sample. The concentric The concentric rings arerings mainly are mainly built ofbuilt a mixture of a mixture of Fe compoundsof Fe compounds with silica with (Figuresilica (Figure4A), whereas 4A), whereas randomly randomly dispersed dispersed pigments pi aregments composed are composed of copper of sulphides copper sulphides (light domain) (light anddomain) Fe-compounds and Fe-compounds (dark domain) (dark (Figuredomain)4D). (Figure 4D).

Minerals 2016, 6, 77 7 of 13 Minerals 2016, 6, 77 7 of 13

FigureFigure 4.4. Backscattered electron (BSE) images of Fe compounds forming different aggregates (A,B,C) andand locallylocally accompaniedaccompanied byby CuCu sulphidessulphides ((DD)) inin agatesagates fromfrom Kerrouchen.Kerrouchen.

4.2.4.2. Raman Microspectroscopy MonocentricMonocentric agatesagates with white and grey bandsbands consistconsist mainlymainly ofof low quartzquartz and subordinatelysubordinately moganitemoganite with distinctive 460 and 501 501 cm cm−´1 1markermarker bands, bands, respectively respectively (Figure (Figure 5).5). Linear Linear mapping mapping of ofthese these agates agates indicated indicated that that moganite moganite is isdistribute distributedd mainly mainly in in darker darker (grey) (grey) regions regions of the agatesagates nodules,nodules, whereaswhereas lowlow quartzquartz isis dominantdominant inin whitewhite regionsregions ofof thethe nodules.nodules. TheseThese agatesagates are are devoid devoid of any of solidany inclusions.solid inclusions. In contrast, In polycentriccontrast, polycentric agates with characteristicagates with browncharacteristic and red brown regions and inside red regions the nodule inside contain the nodule numerous contain Fe-compounds, numerous Fe-compounds, mainly hematite mainly and goethite.hematite Theand presencegoethite. ofThe hematite presence is clearlyof hematite marked is clearly by bands marked at 223, by 245, bands 290, at 408, 223, 498, 245, and 290, 609 408, cm 498,´1 (Tableand 6091; Figurecm−1 (Figure6). The 6). intensive The intensive bands bands at 290, at 290, 408, 408, and and 609 609 cm cm´1−are1 are assigned assigned to toFe-O Fe-O symmetricsymmetric ´1 −1 bendingbending vibrationsvibrations (E (Eg mode),g mode), whereas whereas the weakerthe weaker bands bands at 223 andat 223 498 cmand 498are relatedcm are to symmetricrelated to stretchingsymmetric vibrationsstretching ofvibrations Fe-O (A 1gof)[ Fe–O18]. (A Hematite1g) [18]. Hematite is accompanied is accompanied by carbonaceous by carbonaceous matter marked matter bymarked D-band by atD-band 1320 and at 1320 G-band and atG-band 1585 cm at´ 15851, respectively cm−1, respectively. (Table1). The The band band at at ca. ca. 1320 1320 seems seems to to be be a acombination combination of of two two smaller smaller bands: bands: one one attributed attributed to to carbonaceous carbonaceous matter matter which normally occurs atat 13501350 cmcm´−11 [19][19 ]and and the the second second one one from from hematite hematite which which normally normally appears appears at at about about 1300 1300 cm cm−1 ´[20].1 [20 In]. Inthis this complex complex inclusion inclusion there there are are also also traces traces of of carbonates carbonates (possibly calcite).calcite). TheThe 10851085 cm cm´−11 intensive peakpeak waswas takentaken asas aa markermarker band.band.

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Figure 5. 3D (B) plots of micro-Raman line map of monocentric agate nodule from the center core Figure 5. 3D ( B) plots of micro-Raman line map of monocentric agate nodule from the center core towardstowards the outerthe outer rim rim (A) (A with) with a diagrama diagram showing showing thethe ratio of of the the 501/463 501/463 intensities intensities based based on peak on peak towardsarea the measurements outer rim ( alongA) with the ascan diagram line (C ).showing the ratio of the 501/463 intensities based on peak area measurements along the scan line ((C).).

Figure 6. Microphoto of complex inclusion of hematite, calcite, and organic substance in agate with the related Raman bands. Figure 6. Microphoto of complex inclusion of hematite, calcite, and organic substance in agate with Figure 6. Microphoto of complex inclusion of hematite, calcite, and organic substance in agate with the the related Raman bands. related Raman bands.

Minerals 2016, 6, 77 9 of 13 Minerals 2016, 6, 77 9 of 13 Minerals 2016, 6, 77 9 of 13 Goethite found in agates is evidencedevidenced by markermarker bandsbands atat 297,297, 384,384, 415,415, 548,548, 680,680, 997, and Goethite´1 found in agates is evidenced by marker bands at´ 1297, 384, 415, 548, 680, 997, and 1298 cm−1 (Figure(Table1 7).; Figure The most7). The intensive most intensive band at 384 band cm at−1 384is connected cm is with connected Fe–O–Fe/–OH with Fe-O-Fe/-OH symmetric −1 −1 symmetric1298stretching cm (Figure stretchingvibrations. 7). The vibrations. The most others intensive The are others band attributed are at 384 attributed cmto isFe–OH toconnected Fe-OH symmetric symmetric with Fe–O–Fe/–OH bending bending andand symmetric Fe–OH Fe-OH ´ asymmetricstretching vibrations. stretching vibrations,vibrations,The others respectivelyrespec are tivelyattributed [[18].18]. TheTheto bandsbandsFe–OH atat 203symmetric203 andand 463463 bending cm cm−1 are attributedand Fe–OH to −1 lowasymmetric alpha quartz stretching [[21],21], whichwhichvibrations, isis thethe respec mainmain mineraltivelymineral [18]. componentcomponent The bands ofof agates.atagates. 203 and 463 cm are attributed to low alpha quartz [21], which is the main mineral component of agates.

Figure 7. Microphoto of goethite in agate with its Raman spectrum. Figure 7. Microphoto of goethite in agate with its Raman spectrum. Single crystals of rutile (Figure 8) were also identified within the agates with characteristic Single crystalscrystals of of rutile rutile (Table (Figure1; Figure 8)−1 were8) were also also identified identiﬁed within within the the agates agates with−1 characteristiccharacteristic bands at 141 (B1g), 443 (Eg), and 610 cm ´ (A1g). The distinctive broad band at 241 cm in´ the rutile RS bands at 141 (B ), 443 (E ), and 610 cm−1 1 (A ). The distinctive broad band at 241 cm−1 1 in the rutile bandsspectrum at 141 is a (B second1g), 443 order (Egg), andscattering 610 cm effect (A1g [22].).1g The distinctive broad band at 241 cm in the rutile RS RSspectrum spectrum is a issecond a second order order scattering scattering effect effect [22]. [22 ].

Figure 8. Microphoto of rutile in agate with its Raman spectrum. Figure 8. Microphoto of rutile in agate with its Raman spectrum. Figure 8. Microphoto of rutile in agate with its Raman spectrum. Table 1. Raman bands (cm−1) observed in spectra shown in Figures 6–8. Table 1. Raman bands (cm−1) observed in spectra shown in Figures 6–8. Table 1. Raman bands (cm´1) observed in spectra shown in Figures6–8. Band (cm−1) Assignment References −1 223, 245, 290,Band 408, (cm 498,) 609, 1320 Assignment hematite References [18] Band (cm´1) Assignment References 223, 245, 290,1320, 408, 1585 498, 609, 1320 carbonaceous hematite matter [18][19] 223, 245, 290, 408,1320,1085 498, 1585 609, 1320 carbonaceouscarbonates hematite (calcite?) matter [19][23] [18 ] 297, 384,1320, 415, 15851085548, 680, 997, 1298 carbonaceouscarbonates goethite (calcite?) matter [23] [18] [19 ] 297, 384, 415,141,1085 548, 443, 680, 610 997, 1298 carbonates goethite (possibly rutile calcite) [18][22] [23 ] 297, 384, 415,141, 548, 443, 680, 610 997, 1298 goethite rutile [22] [18 ] 141, 443, 610 rutile [22] 4.3. X-Ray Fluorescence 4.3. X-Ray Fluorescence 4.3. X-RayTwo samples Fluorescence of monocentric and polycentric agate (Figure 2, samples H and D, respectively) wereTwo analysed samples with of XRF monocentric to observe and the distributionpolycentric agateof elements (Figure such 2, samples as Fe, Cu, H Mnand and D, respectively)Ti within the Two samples of monocentric and polycentric agate (Figure2, samples H and D, respectively) wereagate analysedmatrix (Figures with XRF 9–11). to observe For both the samples, distribution titanium of elements and manganese such as Fe,concentrate Cu, Mn and very Ti close within to the were analysed with XRF to observe the distribution of elements such as Fe, Cu, Mn and Ti within agateouter matrixrims of (Figures agate nodules,9–11). For whereas both samples, iron istita alsonium distributed and manganese in the concentrate inner part veryof the close nodules to the outer(Figures rims 9 andof agate11). Copper nodules, is depositedwhereas ironin a rhomboidis also distributed structure inthat the is innerthe core part of ofthe the polycentric nodules (Figures 9 and 11). Copper is deposited in a rhomboid structure that is the core of the polycentric

Minerals 2016, 6, 77 10 of 13 the agate matrix (Figures9–11). For both samples, titanium and manganese concentrate very close to the outer rims of agate nodules, whereas iron is also distributed in the inner part of the nodules Minerals 2016, 6, 77 10 of 13 (FiguresMinerals9 and2016 , 116, 77). Copper is deposited in a rhomboid structure that is the core of the polycentric10 of agate13 and measures around 5 mm in size (Figure9), whereas it is barely detected in the monocentric agate agate and measures around 5 mm in size (Figure 9), whereas it is barely detected in the monocentric (Figureagate 11 and). Positivemeasures correlations around 5 mm were in size observed (Figure between9), whereas manganese it is barely vs.detected iron andin the titanium monocentric in both agate (Figure 11). Positive correlations were observed between manganese vs. iron and titanium in agatesagate (Figures (Figure 10 11). and Positive 12). Interestingly, correlations were for monocentric observed between agates, manganese good correlation vs. iron and between titanium Fe and in Ti both agates (Figures 10 and 12). Interestingly, for monocentric agates, good correlation between Fe wasboth also agates observed (Figures (Figure 10 and 12). 12). There Interestingly, are no correlations for monocentric between agates, Cu and good Mn, correlation though theirbetween analytical Fe and Ti was also observed (Figure 12). There are no correlations between Cu and Mn, though their and Ti was also observed (Figure 12). There are no correlations between Cu and Mn, though their points,analytical forming points, rhombus forming shaped rhombus structures shaped in structures the core of in polycentric the core of agate, polycentric are located agate, near are located each other, analytical points, forming rhombus shaped structures in the core of polycentric agate, are located butnear not ineach the other, same but place not (Figuresin the same9 and place 10 ).(Figures 9 and 10). near each other, but not in the same place (Figures 9 and 10).

FigureFigure 9. 9. The photo of polycentric agate together with maps of characteristic Kα X-rayα intensities Figure The9. The photo photo of of polycentric polycentric agateagate togethertogether with maps maps of of characteristic characteristic Kα K X-rayX-ray intensities intensities showing spatial distribution of Fe, Mn, Ti and Cu. showingshowing spatial spatial distribution distribution of of Fe, Fe, Mn, Mn, Ti Ti and and Cu.Cu.

Figure 10. Correlations between characteristic X-ray intensities of Fe, Mn, Ti and Cu for polycentric agate. Figure 10. Correlations between characteristic X-ray intensities of Fe, Mn, Ti and Cu for polycentric agate. Figure 10. Correlations between characteristic X-ray intensities of Fe, Mn, Ti and Cu for polycentric agate.

Minerals 2016, 6, 77 11 of 13 Minerals 2016, 6, 77 11 of 13 Minerals 2016, 6, 77 11 of 13

FigureFigure 11. The 11. The photo photo of monocentricof monocentric agate agate together together with maps maps of of characteristic characteristic Kα KX-rayα X-ray intensities intensities Figureshowing 11. spatial The photo distribution of monocentric of Fe, Mn, agate Ti and together Cu. with maps of characteristic Kα X-ray intensities showing spatial distribution of Fe, Mn, Ti and Cu. showing spatial distribution of Fe, Mn, Ti and Cu.

Figure 12. Correlations between characteristic X-ray intensities of Fe, Mn, Ti and Cu for monocentric agate. FigureFigure 12.12. CorrelationsCorrelations between between characteristic characteristic X-ray intensities X-ray of intensities Fe, Mn, Ti and of Fe,Cu for Mn, monocentric Ti and agate. Cu for 5. Discussion monocentric agate. 5. Discussion The agates from the Kerrouchen vicinity (Khénifra Province, Meknés-Tafilalet Region), 5. DiscussionoccurringThe agatesin Triassic from basalts, the Kerrouchen display exceptionally vicinity (Khénifrahigh diversity Province, in textural Meknés-Tafilalet features and accessoryRegion), occurringcompounds, in Triassicforming basalts, solid inclusions. display exceptionally They exhibi hight richness diversity in colour, in textural morphology, features and and accessory patterns. Thecompounds,Among agates all agatesfrom forming thevarieties solid Kerrouchen thatinclusions. have vicinity been They found (Khénifraexhibi int thatrichness Province, region in so colour, Meknés-Taﬁlaletfar, three morphology, different Region),morphological and patterns. occurring in TriassicAmonggroups basalts, allof agatesagates display varietieswere exceptionally distinguished: that have been high i.e., found diversitymono in centricthat in region textural (samples so far, features A, three B, differentG, and and accessory H), morphological polycentric compounds, forminggroups(sample solid ofD), inclusions.agates and pseudostalactitic were Theydistinguished: exhibit (samples richnessi.e., C, mono E, F, in centricand colour, I). Rarely,(samples morphology, they A, reveal B, G, andspecific and patterns. H), morphological polycentric Among all agates(samplezones varieties such D), asand that osculum pseudostalactitic have or been aperture. found (samples The in agates that C, regionE, are F, madeand so I). far,up Rarely, of three almost they different tworeveal polymorphs specific morphological morphological of silica, groups i.e., of agateszonesmainly were such low distinguished: asquartz osculum and or subordinately i.e.,aperture. monocentric The moganite, agates (samples are whic madeh under A, up B, of polarizing G, almost and H),two microscope polycentricpolymorphs are (sampleofdescribed silica, i.e., D), as and mainly low quartz and subordinately moganite, which under polarizing microscope are described as pseudostalactiticchalcedony. The (samples content C,of moganite E, F, and within I). Rarely, silica rocks they revealincreases speciﬁc from zero morphological [1] to ~70% [24,25] zones along such as chalcedony.with their maturation The content (vide of moganite [3]). Moxon within and silica Rios rocks [26] increases noted that from maturation zero [1] to of ~70% cryptocrystalline [24,25] along osculum or aperture. The agates are made up of almost two polymorphs of silica, i.e., mainly low withsilica theirphases maturation lowers the (vide moganite [3]). Moxoncontent andover Rios tens [26]of millions noted ofthat years. maturation of cryptocrystalline quartzsilica and phases subordinately lowers themoganite, moganite cont whichent over under tens polarizing of millions microscope of years. are described as chalcedony. The content of moganite within silica rocks increases from zero [1] to ~70% [24,25] along with their maturation (vide [3]). Moxon and Rios [26] noted that maturation of cryptocrystalline silica phases lowers the moganite content over tens of millions of years. Minerals 2016, 6, 77 12 of 13

The silica in agates from Kerrouchen is accompanied by the presence of iron compounds such as hematite and goethite. They occur in a size range from tiny crystals to large aggregates. Fe-oxides and -hydroxides form regular, round, star-like aggregates or laminas sandwiched with pure silica. Locally, they are randomly distributed within the silica matrix. It seems that both Fe as well as Si probably originate from the same source, i.e., low temperature hydrothermal fluids and/or fluids from the alteration of host volcanics (e.g., [4,27]). The distribution of iron within the agates micro-texture might be both of primary or secondary origin. Iron oxides can admixture from amorphous silica during crystallization or can be removed from the silica and accumulated due to the ongoing growth in the growth zones of the gems. The positive correlations between iron vs. manganese, and titanium vs. manganese, are consistent with the geochemistry of these elements observed down to hydrothermal conditions. Agates from Kerrouchen, though macroscopically different from agates from Sidi Rahal, contain a similar wealth of solid inclusions (hematite, goethite, rutile, and copper sulphides) formed during post-magmatic processes at the post magmatic activities (hydrothermal stage). They are the same age (Triassic) and occur in the same rock types (basalts) as agates from Sidi Rahal, so moganite contribution in them is similar (vide [3]). The only feature differentiating these stones is the presence of opal CT (cristobalite-tridymite), which was not identified in agates from Kerrouchen. In spite of some differences, these beautiful Moroccan gems from Sidi Rahal and Kerrouchen seem to have a common origin. Summing up, the formation of agates from Kerrouchen was induced by Si-rich and Fe-moderate fluids. Sparse copper sulphides, titanium oxides as well as calcium carbonates were likely incorporated during post-magmatic processes. The origin of solid bitumen can be of hydrothermal or hypergenic processes by exposure to groundwater [3]. Regardless of its origin, organic matter seems to be a ubiquitous component of many gemstones, including agates [28–31].

Acknowledgments: Jacek Szczerba, Remigiusz Molenda, Andrzej Ku´zmaare gratefully acknowledged for providing the stones for the study. We also thank very much Jens Götze, two other anonymous Reviewers and Fan Wang, the Editor of Minerals, for their constructive criticism as well as friendly and helpful remarks, which significantly improved the manuscript. This work was supported by a research statutory grant No 11.11.140.319 from the AGH University of Science and Technology (Krakow, Poland). Author Contributions: Lucyna Natkaniec-Nowak initiated the investigations of agates, designed the experiments and contributed to writing the paper. Magdalena Dumańska-Słowikanalysed the data of micro-Raman analyses and contributed to writing the paper. Marek Lankosz and Paweł Wróbel performed XRF analyses and analyzed the data. Jaroslav Prsek provided with some materials and prepared the section ‘geological setting’. Adam Gaweł performed microRaman and SEM analyses. Jacek Kocemba made microscopic photos and analyzed the data. Joanna Kowalczyk assisted in editing the text. Conflicts of Interest: The authors declare no conflict of interest.

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