Thalhammerite, Pd9ag2bi2s4, a New Mineral from the Talnakh and Oktyabrsk Deposits, Noril’Sk Region, Russia

Article Thalhammerite, Pd9Ag2Bi2S4, a New Mineral from the Talnakh and Oktyabrsk Deposits, Noril’sk Region, Russia

Anna Vymazalová 1,*, František Laufek 1, Sergey F. Sluzhenikin 2, Vladimir V. Kozlov 3, Chris J. Stanley 4, Jakub Plášil 5, Federica Zaccarini 6, Giorgio Garuti 6 and Ronald Bakker 6

1 Czech Geological Survey, Geologická 6, 152 00 Prague 5, Czech Republic; [email protected] 2 Institute of Geology of Ore Deposits, Mineralogy, Petrography and Geochemistry RAS, Staromonetnyi per. 12, Moscow 119017, Russia; [email protected] 3 Oxford Instruments (Moscow Ofﬁce), 26 Denisovskii Pereulok, Moscow 105005, Russia; [email protected] 4 Department of Earth Sciences, Natural History Museum, London SW7 5BD, UK; [email protected] 5 Institute of Physics, AS CR v.v.i. Na Slovance 2, 182 21 Prague 8, Czech Republic; [email protected] 6 Department of Applied Geosciences and Geophysics, University of Leoben, Peter Tunner Str. 5, A 8700 Leoben, Austria; [email protected] (F.Z.); [email protected] (G.G.); [email protected] (R.B.) * Correspondence: [email protected]; Tel.: +420-251-085-228

Received: 19 July 2018; Accepted: 3 August 2018; Published: 8 August 2018

Abstract: Thalhammerite, Pd9Ag2Bi2S4, is a new sulphide discovered in galena-pyrite-chalcopyrite and millerite-bornite-chalcopyrite vein-disseminated ores from the Komsomolsky mine of the Talnakh and Oktyabrsk deposits, Noril’sk region, Russia. It forms tiny inclusions (from a few µm up to about 40–50 µm) intergrown in galena, chalcopyrite, and also in bornite. Thalhammerite is brittle and has a metallic lustre. In plane-polarized light, thalhammerite is light yellow with weak bireflectance, weak pleochroism, in shades of slightly yellowish brown and weak anisotropy; it exhibits no internal reflections. Reflectance values of thalhammerite in air (R1,R2 in %) are: 41.9/43.0 at 470 nm, 43.9/45.1 at 546 nm, 44.9/46.1 at 589 nm, and 46.3/47.5 at 650 nm. Three spot analyses of thalhammerite give an average composition: Pd 52.61, Bi 22.21, Pb 3.92, Ag 14.37, S 7.69, and Se 0.10, total 100.90 wt %, corresponding to the empirical formula Pd8.46Ag2.28(Bi1.82Pb0.32)Σ2.14(S4.10Se0.02)Σ4.12 based on 17 atoms; the average of five analyses on synthetic thalhammerite is: Pd 55.10, Bi 24.99, Ag 12.75, and S 7.46, total 100.30 wt %, corresponding to Pd8.91Ag2.03Bi2.06S4.00. The density, calculated on the basis of the empirical formula, is 9.72 g/cm3. The mineral is tetragonal, space group I4/mmm, with a 8.0266(2), c 9.1531(2) Å, V 589.70(2) Å3 and Z = 2. The crystal structure was solved and refined from the single-crystal X-ray-diffraction data of synthetic Pd9Ag2Bi2S4. Thalhammerite has no exact structural analogues known in the mineral system; chemically, it is close to coldwellite (Pd3Ag2S) and kravtsovite (PdAg2S). The strongest lines in the X-ray powder diffraction pattern of synthetic thalhammerite [d in Å (I)(hkl)] are: 3.3428(24)(211), 2.8393(46)(220), 2.5685(21)(301), 2.4122(100)(222), 2.3245(61)(123), 2.2873(48)(004), 2.2201(29)(132), 2.0072(40)(400), 1.7481(23)(332), and 1.5085(30)(404). The mineral honours Associate Professor Oskar Thalhammer of the University of Leoben, Austria.

Keywords: thalhammerite; platinum-group mineral; Pd9Ag2Bi2S4 phase; reﬂectance data; X-ray-diffraction data; crystal structure; Komsomolsky mine; Talnakh deposit; Noril’sk region; Russia

1. Introduction

Thalhammerite, ideally Pd9Ag2Bi2S4, was observed in the same holotype specimen as kravtsovite, PdAg2S[1], and vymazalováite, Pd3Bi2S2 [2]. The type sample (polished section) comes from

Minerals 2018, 8, 339; doi:10.3390/min8080339 www.mdpi.com/journal/minerals Minerals 2018, 8, 339 2 of 13 vein-disseminated pyrite-chalcopyrite-galena ore from the Komsomolsky mine in the Talnakh deposit of the Noril’sk district, Russia. The sample was found at coordinates: 69◦3002000 N and 88◦27Minerals01700 E. 2018 The, 8, x mineralization is characterized by lack of Ni minerals and high galena2 of content 14 and Pt-Pd-Ag bearing minerals in an association of pyrite and chalcopyrite. The host rocks of disseminated pyrite-chalcopyrite-galena ore from the Komsomolsky mine in the Talnakh deposit of pyrite-chalcopyrite-galena ore are diopside-hydrogrosssular-serpentine metasomatites developed the Noril’sk district, Russia. The sample was found at coordinates: 69°30′20″ N and 88°27′17″ E. The in diopside-monticellitemineralization is characterized skarns belowby lack theof Ni lower minerals exocontact and high galena of the content Talnakh and intrusion Pt-Pd-Ag (thebearing eastern partminerals of the Komsomolsky in an association mine).of pyrite and Thalhammerite, chalcopyrite. The in host pyrite-chalcopyrite-galena rocks of pyrite-chalcopyrite-galena ores, occurs ore in associationare diopside-hydrogrosssular-serpentine with cooperite, braggite, vysotskite, metasomatites stibiopalladinite, developed telargpalite, in diopside-monticellite sobolevskite, skarns kotulskite, sopcheite,below insizwaite,the lower exocontact kravtsovite, of the vymazalov Talnakh áintrusioite, Au-Agn (the alloys, eastern and part Ag-bearing of the Komsomolsky sulphides, mine). selenides, sulphoselenides,Thalhammerite, and in tellurosulphoselenides.pyrite-chalcopyrite-galena Theores, mineral occurs in was association also observed with cooperite, in vein-disseminated braggite, millerite-bornite-chalcopyritevysotskite, stibiopalladinite, ore telarg frompalite, the sobolevskite, Talnakh and kotulskite, Oktyabrsk sopcheite, deposits insizwaite, of the Noril’sk kravtsovite, region [3]. The hostvymazalováite, rocks of millerite-bornite-chalcopyrite Au-Ag alloys, and Ag-bearing ore are su pyroxene-hornfelslphides, selenides, at thesulphoselenides, lower exocontact and of the Kharaelakhtellurosulphoselenides. intrusion (the westernThe mineral part ofwas the also Komsomolsky observed in mine).vein-disseminated In millerite-bornite-chalcopyrite millerite-bornite- chalcopyrite ore from the Talnakh and Oktyabrsk deposits of the Noril’sk region [3]. The host rocks ore, thalhammerite occurs in association with kotulskite, telargpalite, laﬂammeite, and Au-Ag alloys. of millerite-bornite-chalcopyrite ore are pyroxene-hornfels at the lower exocontact of the Kharaelakh Theintrusion mineral (the likelywestern formed part of underthe Komsomolsky the same conditions mine). In millerite-bornite-chalcopyrite as kravtsovite and vymazalov ore, áite, ◦ withthalhammerite decreasing temperature occurs in association [3], most with likely kotulskite, below telargpalite, 400 C. Thalhammerite laflammeite, and was Au-Ag also alloys. observed, in intergrowthsThe withmineral sobolevskite, likely formed in PGEunder ores the fromsame theconditions Fedorov-Pana as kravtsovite Layered and Intrusive vymazalováite, Complex, with Russia (V.V.decreasing Subbotin—per. temperature communication). [3], most likely Furthermore, below 400 °C. theThalhammerite occurrence was of unknownalso observed, phases in intergrowths corresponding to Pb-with and sobolevskite, Tl-analogues in PGE of thalhammerite ores from the Fedoro from thev-Pana Fedorov-Pana Layered Intrusive Layered Complex, Intrusive Russia Complex (V.V. has beenSubbotin—per. reported [4]. communication). Furthermore, the occurrence of unknown phases corresponding to BothPb- and the Tl-analogues mineral and of namethalhammerite were approved from the by Fedorov-Pana the Commission Layered on Intrusive New Minerals, Complex Nomenclature has been and Classiﬁcationreported [4]. of the International Mineralogical Association (IMA No 2017-111). The mineral Both the mineral and name were approved by the Commission on New Minerals, Nomenclature name is for Dr. Oskar Thalhammer (b. 1956) Associate Professor at the University of Leoben, Austria and Classification of the International Mineralogical Association (IMA No 2017-111). The mineral for hisname contributions is for Dr. Oskar to the Thalhammer ore mineralogy (b. 1956) and Associat minerale Professor deposits at of the platinum University group of Leoben, elements. Austria The type specimenfor his is contributions deposited at to the the Department ore mineralogy of Earthand mi Sciencesneral deposits of the of Natural platinum History group Museum,elements. The London, UK, cataloguetype specimen no. BMis deposited 2016, 150. at the Department of Earth Sciences of the Natural History Museum, London, UK, catalogue no. BM 2016, 150. 2. Appearance, and Physical and Optical Properties 2. Appearance, and Physical and Optical Properties Thalhammerite forms very small inclusions (from a few µm up to about 40–50 µm) in galena, chalcopyriteThalhammerite (Figure1), andforms also very in small bornite. inclusions (from a few μm up to about 40–50 μm) in galena, chalcopyrite (Figure 1), and also in bornite.

(a)

Figure 1. Cont.

Minerals 2018, 8, 339 3 of 13 Minerals 2018, 8, x 3 of 14

(b)

FigureFigure 1. Digital 1. Digital image image in in reﬂected reflected plane planepolarized polarized light showing showing inclusions inclusions of thalhammerite of thalhammerite in in galenagalena (gn) (gn) in association in association with with (a )(a chalcopyrite) chalcopyrite (ccp) (ccp) andand ( (bb)) vymazalováite vymazalováite (vym). (vym).

The mineral occurs in aggregates (100–200 μm in size) formed by intergrowths of telargpalite, Thebraggite, mineral vysotskite, occurs sopcheite, in aggregates stibiopalladinite, (100–200 µ msobolevskite, in size) formed moncheite, by intergrowths kotulskite, malyshevite, of telargpalite, braggite,insizwaite, vysotskite, acanthite, sopcheite, aurian stibiopalladinite,silver, kravtsovite, sobolevskite,and vymazalováite moncheite, in association kotulskite, with malyshevite, galena, insizwaite,chalcopyrite, acanthite, bornite, aurian millerite, silver, and pyrite. kravtsovite, and vymazalováite in association with galena, chalcopyrite,Thalhammerite bornite, millerite, is opaque and with pyrite. a metallic lustre. The mineral is brittle. The density calculated on Thalhammeritethe basis of the empirica is opaquel formula with is a9.72 metallic g/cm3. In lustre. plane-polarized The mineral light, is thalhammerite brittle. The density is light yellow calculated on thewith basis weak of bireflectance, the empirical weak formula pleochroism, is 9.72 in g/cm shades3. of In slightly plane-polarized yellowish br light,own and thalhammerite weak anisotropy. is light yellowIt exhibits with weak no internal bireflectance, reflections. weak pleochroism, in shades of slightly yellowish brown and weak Reflectance measurements were made in air relative to a WTiC standard on both natural and anisotropy. It exhibits no internal reflections. synthetic thalhammerite using a J and M TIDAS diode array spectrometer attached to a Zeiss ReflectanceAxiotron microscope. measurements The results were are made tabulated in air (Table relative 1) and to illustrated a WTiC standardin Figure 2. on both natural and synthetic thalhammerite using a J and M TIDAS diode array spectrometer attached to a Zeiss Axiotron microscope. The resultsTable are tabulated 1. Reflectance (Table data 1for) and natural illustrated and synthetic in Figure thalhammerite.2.

Natural Synthetic Table 1. Reﬂectance data for natural and synthetic thalhammerite. λ (nm) R1 (%) R2 (%) R1 (%) R2 (%) 400 40.0 41.2 40.6 42.1 420 40.6 Natural41.8 41.3 Synthetic42.6 λ (nm) 440 R41.11 (%) 42.3 R2 (%) 42.0 R1 (%)43.2 R2 (%) 460 41.7 42.8 42.6 43.9 400 40.0 41.2 40.6 42.1 420470 41.9 40.6 43.0 41.8 42.9 41.3 44.3 42.6 440480 42.2 41.1 43.3 42.3 43.1 42.0 44.6 43.2 460500 42.7 41.7 43.9 42.8 43.8 42.6 45.3 43.9 470520 43.2 41.9 44.4 43.0 44.6 42.9 46.0 44.3 480540 43.7 42.2 44.9 43.3 45.3 43.1 46.6 44.6 500546 43.9 42.7 45.1 43.9 45.6 43.8 46.9 45.3 520560 44.2 43.2 45.4 44.4 45.9 44.6 47.2 46.0 540580 44.7 43.7 45.9 44.9 46.4 45.3 47.7 46.6 546 43.9 45.1 45.6 46.9 589 44.9 46.1 46.7 47.9 560 44.2 45.4 45.9 47.2 600 45.2 46.3 46.9 48.1 580 44.7 45.9 46.4 47.7 589620 45.6 44.9 46.8 46.1 47.3 46.7 48.5 47.9 600 45.2 46.3 46.9 48.1 620 45.6 46.8 47.3 48.5 640 46.1 47.3 47.7 48.9 Minerals 2018, 8, 339 4 of 13

Table 1. Cont.

Minerals 2018, 8, x Natural Synthetic 4 of 14 λ (nm) R1 (%) R2 (%) R1 (%) R2 (%) 640 46.1 47.3 47.7 48.9 650650 46.346.3 47.5 47.5 47.9 47.9 49.1 49.1 660660 46.546.5 47.8 47.8 48.0 48.0 49.2 49.2 680680 47.047.0 48.3 48.3 48.3 48.3 49.5 49.5 700700 47.447.4 48.9 48.9 48.6 48.6 49.8 49.8 Note.Note.The The values values required required by by the the Commission Commission on onOre Ore Mineralogy Mineralogyare aregiven givenin inbold. bold.

FigureFigure 2. Reﬂectance 2. Reflectance data data for for thalhammerite thalhammerite compared compared to synthetic synthetic analogue, analogue, in air. in air.The Thereflectance reﬂectance values (R%) are plotted versus the wavelength λ in nm. values (R%) are plotted versus the wavelength λ in nm. 3. Chemical Composition 3. Chemical Composition Electron probe micro-analyses (EPMA) on grains of thalhammerite were obtained using a WDA ElectronInca Wave probe 500 micro-analyses(Oxford Instruments (EPMA) NanoAnalysis, on grains High of thalhammerite Wycombe, UK) wereinstalled obtained on an SEM using Lyra aWDA Inca Wave3GM 500 (Tescan), (Oxford with Instruments analytical conditions NanoAnalysis, of 20 HighkV, 10 Wycombe, nA, and counting UK) installed times onof 30 an s SEM (on Lyrapeak 3GM (Tescan),positions)/2 with analytical × 15 s (background conditions on of the 20 left kV, and 10 right nA, andpositions). counting The spectra times ofwere 30 collected s (on peak on positions)/PbMα, 2 × 15BiM s (backgroundα, PdLα, AgLα, on SK theα, and left SeL andα lines right with positions). standards Theof pure spectra Se, Pd, were Ag, collectedBi, synthetic on PbTe, PbM andα, BiM α, natural FeS2. Other elements were below the detection limit. PdLα, AgLα, SKα, and SeLα lines with standards of pure Se, Pd, Ag, Bi, synthetic PbTe, and natural EPMA on synthetic thalhammerite were obtained using a CAMECA SX-100 electron probe FeS . Other elements were below the detection limit. 2 microanalyzer in wavelength-dispersive mode with an electron beam focussed to 1–2 μm. EPMA on synthetic thalhammerite were obtained using a CAMECA SX-100 electron probe Pure elements and ZnS were used as standards and the radiations measured were BiMα PdLα, microanalyzerAgLα, and in SK wavelength-dispersiveα, with an accelerating voltage mode of with 15 kV, an and electron a beam beam current focussed of 10 nA to measured 1–2 µm. on the PureFaraday elements cup. and ZnS were used as standards and the radiations measured were BiMα PdLα, AgLα, andEPMA SKα, withcompared an accelerating with literature voltage data are of given 15 kV, in andTable a 2. beam The empirical current offormulae 10 nA calculated measured on on the Faradaythe cup. basis of 17 apfu are Pd8.46Ag2.28(Bi1.82Pb0.32)Σ2.14(S4.10Se0.02)Σ4.12 for thalhammerite and Pd8.91Ag2.03Bi2.06S4.00 for EPMAits synthetic compared analogue, with with literature the ideal data formulae are givenPd9Ag2 inBi2 TableS4. 2. The empirical formulae calculated apfu on the basis of 17Table 2. areElectron-microprobe Pd8.46Ag2.28(Bi analyses1.82Pb of0.32 natural)Σ2.14 and(S4.10 syntheticSe0.02 thalhammerite.)Σ4.12 for thalhammerite and Pd8.91Ag2.03Bi2.06S4.00 for its synthetic analogue, with the ideal formulae Pd9Ag2Bi2S4. wt % Pd Ag Pb Bi S Se Total ThalhammeriteTable 2. Electron-microprobe analyses of natural and synthetic thalhammerite. 52.80 14.57 2.60 22.56 7.75 0.07 100.35 53.40 14.29 3.05 22.09 7.62 0.03 100.47 wt % Pd Ag Pb Bi S Se Total 51.64 14.25 6.12 21.98 7.70 0.19 101.87 average Thalhammerite52.61 14.37 3.92 22.21 7.69 0.10 100.90 13/B-92 * 53.85 52.8012.51 14.57 2.60 22.5624.84 7.757.90 0.07100.35 99.1 52.77 53.4012.27 14.291.77 3.05 22.0924.29 7.627.45 0.030.57 100.47 99.12 1/K-92 * 53.85 51.6412.8 14.25 6.12 21.9824.24 7.707.89 0.19101.87 99.01 average52.77 52.6111.83 14.37 3.92 22.2125.73 7.697.99 0.10100.90 99.53 13/B-92 * 53.85 12.51 24.84 7.90 99.1 54.08 12.21 25.34 7.95 101.21 52.77 12.27 1.77 24.29 7.45 0.57 99.12

Minerals 2018, 8, 339 5 of 13

Table 2. Cont.

wt % Pd Ag Pb Bi S Se Total Thalhammerite 1/K-92 * 53.85 12.8 24.24 7.89 99.01 52.77 11.83 25.73 7.99 99.53 54.08 12.21 25.34 7.95 101.21 Synthetic Sample Exp37 54.18 13.69 25.02 7.59 100.48 54.74 12.91 25.04 7.50 100.19 54.66 12.46 25.90 7.39 100.42 56.14 12.01 24.70 7.36 100.21 55.78 12.67 24.27 7.44 100.16 55.10 12.75 24.99 7.46 100.29 average 55.10 12.75 24.99 7.46 100.30 * Sluzhenikin and Mohkov [2].

4. Synthetic Analogue The small size of thalhammerite embedded in galena (bornite) prevented its extraction and isolation in an amount sufﬁcient for the relevant crystallographic and structural investigations. Therefore, these investigations were performed on the synthetic Pd9Ag2Bi2S4. The synthetic phase of Pd9Ag2Bi2S4 was prepared in an evacuated and sealed silica-glass tube in a horizontal furnace in the Laboratory of Experimental Mineralogy of the Czech Geological Survey in Prague. To prevent loss of material to the vapour phase during the experiment, the free space in the tube was reduced by placing a closely-ﬁtting silica glass rod against the charge. The temperature was measured with Pt-PtRh thermocouples and is accurate to within ±3 ◦C. A charge of about 300 mg was carefully weighed out from the native elements. We used, as starting chemicals, palladium (99.95%), silver (99.999%), bismuth (99.999%), and sulphur (99.999%). The starting mixture was sealed and annealed, quenched, and then ground in an agate mortar under acetone and reheated to 350 ◦C for 134 days. The sample was quenched by dropping the capsule in cold water.

5. X-ray Crystallography

5.1. Single-Crystal X-ray Diffraction

A small fragment of synthetic Pd9Ag2Bi2S4 was mounted on a glass fibre and examined using a Rigaku Super Nova single-crystal diffractometer with an Atlas S2 CCD detector utilizing MoKα radiation, provided by the microfocus X-ray tube and monochromatized by primary mirror optics. The ω rotational scans were used for collection of three-dimensional intensity data. From a total of 3659 reflections, 221 were classified as unique observed with I > 3ρ(I). Corrections for background, Lorentz effects and polarization were applied during data reduction with the CrysAlis software. Empirical absorption correction was performed using the same software yielding Rint = 0.034. The crystal structure was solved with a charge-flipping method using the program Superflip [5] and subsequently refined by the full-matrix least-squares algorithm of JANA2006 program [6]. Because of the similarity of atomic number of Pd and Ag (46 and 47, respectively), it is nearly impossible to distinguish between these atoms from single-crystal (MoKα radiation) diffraction data. The refinement indicated five metallic positions, which one of them was assigned as Bi. The remaining metallic sites show multiplicities 2:8:8:4. Considering the empirical chemical composition Pd8.91Ag2.03Bi2.06S4.00 (Z = 2) and coordination environment of the 4e site, which was very different from the others (see structure description), the 4e site was refined as Ag position. Next, refinement cycles included all anisotropic displacement parameters, which revealed too large a value for Pd(2) position 2 2 (Ueq(Pd2) = 0.0146 Å cf. 0.0082 and 0.080 Å for Pd(1) and Pd(3), respectively). Refinement of occupancy factors yielded 0.88 occupancy for the Pd(2) position; other positions were found to be fully occupied. Final refinement in the I4/mmm space group for 21 parameters converged smoothly to the Minerals 2018, 8, 339 6 of 13

R = 0.0310 and wR = 0.0815 for 221 observed reﬂections. Details of data collection, crystallographic data, and reﬁnement are given in Table3.

Table 3. Crystallographic data for the selected crystal of synthetic thalhammerite, Pd9Ag2Bi2S4.

Crystal Data

Chemical formula (idealized) Pd9Ag2Bi2S4 Space group I4/mmm (No. 139) a [Å] 8.0266(2) c [Å] 9.1531(2) V [Å3] 589.70(2) Z 2 Crystal size (mm) 0.034 × 0.027 × 0.013 Data Collection Diffractometer SuperNova Temperature (K) 293 Radiation MoKα (0.7107 Å) Theta range (◦) 5.08–27.62 Reflections collected 3659 Independent reflections 226 Unique observed reflections [I > 3(σ)] 221 −10 < h < 10 Index ranges −10 < k < 10 −11 < l < 11 Absorption correction method Empirical Structure Refinement Refinement method Full matrix least-squares on F2 Parameters/restrains/constrains 21/0/0 R, wR (obs) 0.0310/0.0815 R, wR (all) 0.0318/0.0817 Largest diff. peak and hole (e−/Å3) 1.20/−5.20

Atom coordinates and displacement parameters are listed in Table4. Table5 shows selected bond lengths.

Table 4. Fractional coordinates and anisotropic displacement parameters (Å2) for synthetic thalhammerite.

Atom Pd(1) Pd(2) * Pd(3) Ag Bi S Wyckoff 2a 8f 8j 4e 4d 8h Position x 1/2 1/4 1/2 1/2 1/2 0.2081(4) y 1/2 1/4 0.2027(2) 1/2 0 0.2081(4) z 1/2 1/4 0 0.1810(2) 1/4 0 U11 0.0069(8) 0.0104(8) 0.0077(7) 0.0098(6) 0.0090(4) 0.0071(12) U22 0.0069(8) 0.0104(8) 0.0097(7) 0.0098(6) 0.0090(4) 0.0071(12) U33 0.0109(13) 0.0051(10) 0.0077(7) 0.0082(9) 0.0079(6) 0.012(2) U12 0 0.0017(6) 0 0 0 −0.0018(15) U13 0 0.0011(4) 0 0 0 0 U23 0 0.0011(4) 0 0 0 0 Ueq 0.0083(6) 0.0086(5 0.0084(4) 0.0106(4) 0.0086(3) 0.0087(9) * Reﬁned with 0.88 occupancy.

Table 5. Selected bond distances (Å) in the thalhammerite crystal structure.

Pd(1) 4 × S 2.362(3) Ag 4 × Pd(3) 2.905(1) 2 × Ag 2.919(2) 4 × Pd(2) 2.9073(4) Pd(2) 2 × S 2.3372(7) 2 × Bi 2.8378(1) Bi1 4 × Pd(3) 2.808(1) 2 × Ag 2.9073(4) 4 × Pd(2) 2.8378(1) 4 × Pd(3) 3.0670(2) Minerals 2018, 8, 339 7 of 13

Table 5. Cont.

Pd(3) 2 × S 2.343(3) 2 × Bi 2.8080(8) 2 × Ag 2.905(2) 4 × Pd(2) 3.0670(2)

Minerals 2018, 8, x 7 of 14 It should be noted that the refined tetragonal structure model of thalhammerite is only a substructure. As was revealed2 × Ag by subsequent2.905(2) Rietveld refinement (see below), the powder X-ray diffraction pattern of synthetic4 × Pd(2) thalhammerite 3.0670(2) shows at medium and high diffraction angles a few very weak unindexed peaks and very subtle peak splitting, which cannot be fitted using the It should be noted that the refined tetragonal structure model of thalhammerite is only a tetragonalsubstructure. model. As Attemptswas revealed to refine by subsequent the structure Rietveld from refinement single-crystal (see be datalow), in the rhombic powder subgroups X-ray of I4/mmmdiffraction(i.e., patternFmmm ,ofImmm synthetic) led thalhammerite to negligible loweringshows at ofmediumR-factors and (e.g.,high fromdiffraction 0.0313 angles to 0.0293) a few with a rapidvery increase weak unindexed of the refined peaks and parameters very subtle and peak correlations splitting, which between cannot them. be fitted Refinements using the tetragonal in monoclinic subgroupsmodel. Attempts failed. Additionally,to refine the structure neither from of these single-crystal low-symmetry data in rhombic models subgroups describe all of peakI4/mmm splitting observed(i.e., Fmmm in powder, Immm) diffraction led to negligible patterns lowering of synthetic of R-factors thalhammerite. (e.g., from 0.0313 Therefore, to 0.0293) we proposedwith a rapid only the tetragonalincrease averageof the refined substructure parameters of and thalhammerite, correlations between leaving them. some Refinements aspects in of monoclinic the structure subgroups unclear. failed. Additionally, neither of these low-symmetry models describe all peak splitting observed in 5.2.powder Powder diffraction X-ray Ddiffraction patterns of synthetic thalhammerite. Therefore, we proposed only the tetragonal average substructure of thalhammerite, leaving some aspects of the structure unclear. The powder XRD pattern of synthetic thalhammerite was collected in the Bragg-Brentano geometry5.2. Powder on X-ray a Bruker Ddiffraction D8 Advance diffractometer equipped with the LynxEye XE detector and α ◦ ◦ θ ◦ CuK radiation.The powder The XRD data pattern were collectedof synthetic in thethalhamme range fromrite was 10 collectedto 100 2in withthe Bragg-Brentano a step size of 0.005 2θ andgeometry 2 s counting on a Bruker time D8 per Advance step. Thediffractometer structure equipped model obtained with the LynxEye from a single-crystal XE detector and XRD CuK studyα of syntheticradiation. thalhammerite The data were was collected used as in athe starting range structuralfrom 10° tomodel 100° 2θ in with the a subsequent step size of Rietveld0.005° 2θrefinement. and The2 FullProfs counting program time per [step.7] was The used structure and model the pseudo-Voigt obtained from function a single-crystal was used XRD to study generate of synthetic the shape of thethalhammerite diffraction peaks. was used The as refined a starting parameters structural include model in those the subsequent describing Rietveld peak shape refinement. and width, The peak asymmetry,FullProf program unit-cell [7] parameters, was used and the the occupancypseudo-Voigt parameter function was of theused Pd(2) to generate position, the shape and sixof the isotropic displacementdiffraction peaks. parameters. The refined parameters include those describing peak shape and width, peak asymmetry,In total, 17 unit-cell parameters parameters, were refined.the occupancy No fractional parameter coordinates of the Pd(2) were position, refined. and Thesix isotropic final cycles of displacement parameters. Rietveld refinement converged to the agreement factors R = 0.077 and R = 0.115. The refinement In total, 17 parameters were refined. No fractional coordinatesp were refined.wp The final cycles of indicated 7 wt % Pd Bi S (I2 3) impurity in the investigated sample. Rietveld refinement3 converged2 2 1 to the agreement factors Rp = 0.077 and Rwp = 0.115. The refinement indicatedFigure3 7 depicts wt % Pd two3Bi2S2 details(I213) impurity of final in Rietveld the investigated plot showing sample. weak, however discernible, peak ◦ splittingFigure at middle 3 depicts and two high details diffraction of final angles Rietveld of 2plotθ (i.e., showing above weak, 50 ). Attemptshowever discernible, to index all peak observed diffractionssplitting at in middle the powder and high pattern diffraction in the angles large and/orof 2θ (i.e., lower above symmetry 50°). Attempts unit-cell to index remained all observed unsuccessful and,diffractions therefore, in the the structurepowder pattern refinement in the large was and/or limited lower to the symmetry tetragonal unit-cell substructure. remained unsuccessful Table6 presents powderand, therefore, diffraction the data structure for thalhammerite. refinement was limited to the tetragonal substructure. Table 6 presents powder diffraction data for thalhammerite.

FigureFigure 3. Details3. Details of of the theRietveld Rietveld profiles profiles of of synthetic synthetic thalhammerite thalhammerite showing showing the weak the weakpeak splitting, peak splitting, whichwhich cannot cannot be be fitted fitted using using thethe tetragonaltetragonal cell. cell. The The observed observed (circles), (circles), calculated calculated (solid), (solid), and difference and difference profilesprofiles are are shown. shown. The The vertical vertical bars correspond correspond to to Bragg Bragg reflections. reflections.

6. Structure Description The tetragonal substructure of thalhammerite contains three Pd, one Ag, Bi, and S sites, respectively. All sites, except the Pd(2) position, were found to be fully occupied. Its crystal structure is shown in Figure 4.

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FigureFigure 4. 4.Crystal Crystal structure structure of of thalhammerite thalhammerite showing showing the the [PdS [PdS4]4] squares squares and and Pd–S Pd–S bonds. bonds. Unit-cell Unit-cell edgesedges are are highlighted. highlighted. Details Details show show the the Rietveld Rietveld proﬁles profiles of synthetic of synthetic thalhammerite thalhammerite showing showing the weak the peakweak splitting, peak splitting, which cannotwhich cannot be ﬁtted be using fitted the using tetragonal the tetragonal cell. cell.

6.1.6.1. CoordinationCoordination ofof CationsCations TheThe Pd(1)Pd(1) positionposition isis inin thethe centrecentre ofof regularregular squaresquare ofof SS atomsatoms withwith Pd(1)-SPd(1)-S distancesdistances ofof 2.362(3)2.362(3) Å.Å. TheThe coordination coordination is is perfectly perfectly planar. planar. Similar Similar coordination coordination was was observed observed in in vysotskite, vysotskite, PdS PdS [ 8[8],], whichwhich showsshows similar similar Pd–S Pd–S separation separation of of 2.34 2.34 Å. Å. Such Such coordination coordination geometry geometry is is typical typical for for low-spin low-spin 4 d48d8Pd Pd2+2+ cationcation in in normal normal sulﬁdes sulfides with with M:S M:S ratio ratio equal equal to or to smaller or smaller to one to [9 ].one The [9]. Pd(1) The coordination Pd(1) coordination is further is completedfurther completed by two Ag by atomstwo Ag at atoms 2.919(2) at Å2.919(2) lying perpendicularÅ lying perpendicular to the [M(1)S to the4] [M(1)S squares.4] squares. TheThe Pd(2)Pd(2) (reﬁned(refined toto 0.88 0.88 occupancy occupancy of of Pd) Pd) and and Pd(3) Pd(3) sites sites form form complex complex polyhedron. polyhedron. BothBoth PdPd positionspositions areare coordinatedcoordinated byby two S atoms at at distances distances 2.3372(7) 2.3372(7) and and 2.343(3) 2.343(3) Å, Å, a avalue value very very close close to tothe the Pd–S Pd–S distance distance of 2.334(4) of 2.334(4) Å observed Å observed for the for zig-zag the chainszig-zag inchains the structure in the structureof kravtsovite, of kravtsovite, PdAg2S [1]. PdAgWhereas2S[1 the]. Whereas S–Pd(2)–S the group S–Pd(2)–S is perfectly group linear, is perfectly the S–Pd(3)–S linear, the shows S–Pd(3)–S a bonding shows angle a bonding of 177.9(1)°. angle ofPd(2) 177.9(1) is further◦. Pd(2) coordinated is further by coordinated two Bi (2.8378(1) by two Å), Bi two (2.8378(1) Ag (2.9073(4) Å), two Å), Ag and (2.9073(4) two Pd(3) Å), (3.0670(2) and two Pd(3)Å) atoms. (3.0670(2) Pd(3) Å) also atoms. shows Pd(3) two also Bi (2.8080(8) shows two Å), Bi two (2.8080(8) Ag (2.905(2) Å), two Å), Ag and (2.905(2) four Pd(3) Å), and (3.0670(2) four Pd(3) Å) (3.0670(2)short contacts. Å) short contacts. AgAg site site is is surrounded surrounded by by nine nine Pd Pd atoms atoms (Figure (Figure5 )5) forming forming a a mono-capped mono-capped tetragonal tetragonal antiprismatic antiprismatic coordination.coordination. TheThe Ag–PdAg–Pd distancesdistances areare inin thethe rangerange ofof 2.905(1)2.905(1) ÅÅ toto2.919(2) 2.919(2) Å,Å, comparable comparable toto thosethose observedobserved inin lukkulaisvaaraitelukkulaisvaaraite (Pd–Ag:(Pd–Ag: 2.891(4)–3.037(4)2.891(4)–3.037(4) Å;Å; [[10],10], wherewhere AgAg atomsatoms displaydisplay tetragonaltetragonal antiprismaticantiprismatic coordination. coordination. AsAs is is shown shown in in Figure Figure5, the 5, Bithe atom Bi atom is coordinated is coordinated by eight by Pd eigh atomst Pd to atoms form ato bi-capped form a bi-capped trigonal prismtrigonal with prism Bi–Pd with bond Bi–Pd distances bond distances ranging ranging from 2.808(1) from 2.808(1) to 2.8378(1) to 2.8378(1) Å, values Å, values slightly slightly shorter shorter than thosethan those observed observed in structure in structure of monoclinic of monoclinic PdBi (2.84–2.95)PdBi (2.84–2.95) Å; [11 Å;].There [11]. There are no are short no (<3.5short Å)(<3.5 Bi–S Å) contactsBi–S contacts in the thalhammeritein the thalhammerite crystal structure.crystal structur This contrastse. This contrasts with the with environment the environment of Bi in structure of Bi in ofstructure chemically-related of chemically-related vymazalov vymazalováite,áite, Pd3Bi2S2 [2 Pd,123],Bi where2S2 [2,12], Bi atoms where show Bi atoms one additionalshow one additional S contact at S 3.22(3)contact Å. at 3.22(3) Å.

Table 6. X-ray powder diffraction data of thalhammerite (CuKα radiation, Bruker D8 Advance,

Bragg-Brentano geometry). Only reflections with I(obs) ≥ 1 are listed.

I(obs) h k l d(meas) d(calc) 11 1 0 1 6.0364 6.0338 11 1 1 0 5.6790 5.6767 13 0 0 2 4.5752 4.5736 8 2 0 0 4.0155 4.0140

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Minerals 2018, 8, 339 18 1 1 2 3.5620 3.5615 9 of 13 24 2 1 1 3.3428 3.3420 2 2 0 2 3.0181 3.0169 Table 6. X-ray powder9 diffraction 1 data0 of thalhammerite3 2.8510 (Cu Kα 2.8504radiation, Bruker D8 Advance, Bragg-Brentano geometry).46 Only2 reﬂections 2 with0 I(obs) ≥2.83931 are listed.2.8383 21 3 0 1 2.5685 2.5684 I(obs)100 h2 2 k2 l2.4122 d (meas) 2.4117 d(calc) 11 61 11 2 03 12.3245 6.0364 2.3241 6.0338 11 1 1 0 5.6790 5.6767 48 0 0 4 2.2873 2.2868 13 0 0 2 4.5752 4.5736 8 29 21 3 02 02.2201 4.0155 2.2197 4.0140 18 2 12 3 11 22.1637 3.5620 2.1634 3.5615 24 2 1 1 3.3428 3.3420 17 1 1 4 2.1213 2.1212 2 2 0 2 3.0181 3.0169 9 40 14 0 00 32.0072 2.8510 2.0070 2.8504 46 3 23 3 20 01.8923 2.8393 1.8922 2.8383 21 3 0 1 2.5685 2.5684 1008 24 0 22 21.8377 2.4122 1.8378 2.4117 6115 12 3 23 31.7981 2.3245 1.7982 2.3241 4818 02 2 04 41.7805 2.2873 1.7807 2.2868 29 1 3 2 2.2201 2.2197 223 23 3 32 11.7481 2.1637 1.7485 2.1634 174 11 3 14 41.6991 2.1213 1.6991 2.1212 402 44 2 02 01.6711 2.0072 1.6710 2.0070 3 3 3 0 1.8923 1.8922 85 41 4 03 21.6413 1.8377 1.6410 1.8378 151 22 1 35 31.6299 1.7981 1.6300 1.7982 184 24 3 21 41.5814 1.7805 1.5814 1.7807 23 3 3 2 1.7481 1.7485 41 15 1 30 41.5743 1.6991 1.5744 1.6991 28 40 3 25 21.5102 1.6711 1.5103 1.6710 5 1 4 3 1.6413 1.6410 30 4 0 4 1.5085 1.5085 1 2 1 5 1.6299 1.6300 49 41 1 36 11.4723 1.5814 1.4724 1.5814 113 54 4 10 01.4193 1.5743 1.4192 1.5744 8 0 3 5 1.5102 1.5103 7 4 4 2 1.3554 1.3554 30 4 0 4 1.5085 1.5085 912 12 2 16 61.3431 1.4723 1.3431 1.4724 139 42 5 43 01.3395 1.4193 1.3393 1.4192 7 4 4 2 1.3554 1.3554 121 23 5 22 61.3185 1.3431 1.3184 1.3431 919 23 1 56 31.3070 1.3395 1.3070 1.3393 17 31 5 54 21.2969 1.3185 1.2968 1.3184 19 3 1 6 1.3070 1.3070 79 16 2 50 41.2694 1.2969 1.2693 1.2968 93 61 2 27 01.2279 1.2694 1.2279 1.2693 318 16 2 22 71.2231 1.2279 1.2231 1.2279 18 6 2 2 1.2231 1.2231 11 11 6 63 31.2113 1.2113 1.2112 1.2112 1010 44 4 44 41.2059 1.2059 1.2058 1.2058 1111 33 3 36 61.1872 1.1872 1.1871 1.1871

. Figure 5. Coordination polyhedra of Ag (mono-capped tetragonal antiprism) and Bi (bi-capped trigonal Figure 5. Coordination polyhedra of Ag (mono-capped tetragonal antiprism) and Bi (bi-capped prism) in the thalhammerite structure. trigonal prism) in the thalhammerite structure.

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Minerals 2018, 8, x 10 of 14 6.2. Modular Description 6.2. Modular Description The thalhamerite crystal structure forms a three-dimensional framework. It contains features typicalThe for thalhamerite intermetallic crystal compounds structure (e.g., forms complex a three- crystallochemicaldimensional framework. environment It contains of metals) features and, therefore,typical for cannot intermetallic be presented compounds using a traditional(e.g., complex cation-based crystallochemical coordination environment polyhedra of approach. metals) and, therefore,Alternatively, cannot be the presented structure ofusing thalhammerite a traditiona canl cation-based be conveniently coordination described polyhedra as an arrangement approach. of two typesAlternatively, of building the blocks structure (cuboids) of thalhammerite having common can Sbe atoms conveniently at the corners described (Figure as 6an). arrangement of two types of building blocks (cuboids) having common S atoms at the corners (Figure 6). The ﬁrst block (green in Figure6) contains the [PdS 4] squares forming one face of the block and Ag atomsThe infirst its block centre. (green Pd atoms in Figure are approximately6) contains the located[PdS4] squares to the midpoints forming one of the face longer of the S-S block edges. and TheAg secondatoms in block its centre. (orange Pd in atoms Figure are6) containsapproximately Bi atoms located in its to centre. the midpoints By analogy of the with longer the ﬁrst S-S block, edges. theThe Pd second atoms block are located (orange to thein Figure midpoints 6) contains of the longerBi atoms S–S in edges. its centre. In the By thalhammerite analogy with structure,the first block, two typesthe Pd of atoms block alternateare located in to a chess-boarthe midpoints fashion of the within longer the S–S (001) edges. plane In andthe thalhammerite form chains along structure, the c axistwo (Figure types of6). block It should alternate be mentioned in a chess-boar that, neglecting fashion within the Ag the and (001) Bi atoms,plane and the packingform chains of the along green the blocksc axis automatically(Figure 6). It should generates be theirmentioned duals, andthat, the neglecting orange block, the Ag vice and versa. Bi atoms, the packing of the green blocks automatically generates their duals, and the orange block, vice versa.

FigureFigure 6. 6.( a(a)) Arrangement Arrangement of of two two types types of of building building blocks blocks in in the the thalhammerite thalhammerite structure. structure. ( b(b)) Detailed Detailed viewview showing showing the the block block containing containing Ag Ag (green) (green) and and Bi Bi (orange) (orange) atoms. atoms.

6.3.6.3. Relation Relation to to Other Other Minerals Minerals TheThe thalhammerite thalhammerite structurestructure representsrepresents aa unique structure type, and and no no exact exact structural structural analogue analogue is ishitherto hitherto known. known. It Itis is worth worth noting noting that that its its st structureructure merges structurestructure motivesmotives typicaltypical forfor polarpolar chalcogenideschalcogenides and and intermetallic intermetallic compounds. compounds. The The [Pd(1)S [Pd(1)S4]4] square-planar square-planar coordination coordination is is a a hallmark hallmark ofof Pd-bearingPd-bearing sulfides sulﬁdes with with an an M:S M:S ra ratiotio equal equal to, to,or slightly or slightly smaller smaller than, than,one. Contrary one. Contrary to that, to(almost) that, (almost)linear coordination linear coordination of Pd by oftwo Pd S byatoms two and S atoms numb ander of number further ofmetal-metal further metal-metal contacts resulting contacts in resultingcomplex in coordination complex coordination geometry, geometry, can be observed can be observed in sulphides in sulphides with intermetallic with intermetallic behaviour behaviour (e.g., (e.g.,kravtsovite kravtsovite PdAg PdAg2S, Vymazalová2S, Vymazalov et al.,á et 2017 al., 2017 [1]). [1]). AnotherAnother chemically-related chemically-related mineral, mineral, coldwellite, coldwellite, Pd Pd3Ag3Ag2S2S (McDonald(McDonald et et al., al., 2015 2015 [ 13[13]),]), adopts adopts a a cubiccubicβ β-Mn-like-Mn-like structure structure and, and, hence, hence, differs differs substantially substantially from from that that of of thalhammerite. thalhammerite. 7. Proof of Identity of Natural and Synthetic Thalhammerite 7. Proof of Identity of Natural and Synthetic Thalhammerite The structural identity between the synthetic Pd9Ag2Bi2S4 and the natural material was conﬁrmed The structural identity between the synthetic Pd9Ag2Bi2S4 and the natural material was by electron back-scattering diffraction (EBSD) and Raman spectroscopy. confirmed by electron back-scattering diffraction (EBSD) and Raman spectroscopy.

7.1. Electron Back-Scattering Diffraction

Minerals 2018, 8, 339 11 of 13

7.1. Electron Back-Scattering Diffraction Minerals 2018, 8, x 11 of 14 The structural identity between the natural material and the synthetic Pd9Ag2Bi2S4 was confirmed by EBSD. AThe TESCAN structural Lyraidentity 3GM between field the emission natural material scanning and electronthe synthetic microscope Pd9Ag2Bi2S4 combined was confirmed with by EBSD systemEBSD. (Oxford A TESCAN Instruments Lyra 3GM AztecHKL field emission system scanni withng NordlysNano electron microscope EBSD camera)combined was with used EBSD for the measurements.system (Oxford The surface Instruments of natural AztecHKL sample system was with prepared NordlysNano for investigation EBSD camera) by broad was used beam for argon the ion measurements. The surface of natural sample was prepared for investigation by broad beam argon milling using Gatan PECS II system operated at 1 kV. The solid angles calculated from the patterns were ion milling using Gatan PECS II system operated at 1 kV. The solid angles calculated from the compared with our structural model for Pd Ag Bi S synthetic phase match containing 12 reflectors patterns were compared with our structural9 model2 2 for4 Pd9Ag2Bi2S4 synthetic phase match containing to index12 reflectors the patters. to index The the EBSD patters. patterns The EBSD (also pattern knowns (also as Kikuchi known as patterns) Kikuchi patterns) obtained obtained from the from natural materialthe (>50 natural measurements material (>50 onmeasurements different spots on differ on naturalent spots thalhammerite on natural thalhammerite grains) were grains) found were to match the patternsfound to generated match the from patterns our generated structural from model our for structural Pd9Ag 2modelBi2S4 forsynthetic Pd9Ag2Bi phase,2S4 synthetic Figure phase,7. Figure 7.

Figure 7. EBSD image of natural thalhammerite; in the right pane, the Kikuchi bands are indexed. Minerals 2018, 8, x 12 of 14 Minerals 2018, 8, 339 12 of 13

Figure 7. EBSD image of natural thalhammerite; in the right pane, the Kikuchi bands are indexed. The values of the mean angular deviation (MAD, i.e., goodness of ﬁt of the solution) between The values of the mean angular deviation (MAD, i.e., goodness of fit of the solution) between the calculated and measured Kikuchi bands range between 0.22◦ and 0.48◦. These values reveal a the calculated and measured Kikuchi bands range between 0.22° and 0.48°. These values reveal a very very good match; as long as values of mean angular deviation are less than 1◦, they are considered as good match; as long as values of mean angular deviation are less than 1°, they are considered as indicators of an acceptable ﬁt (HKL Technology, 2004). indicators of an acceptable fit (HKL Technology, 2004). 7.2. Raman Spectroscopy 7.2. Raman Spectroscopy The Raman spectroscopy technique was applied to verify the structural identity between the The Raman spectroscopy technique was applied to verify the structural identity between the synthetic Pd9Ag2Bi2S4 and the natural material (Figure8). synthetic Pd9Ag2Bi2S4 and the natural material (Figure 8).

FigureFigure 8.8. ComparisonComparison ofof RamanRaman spectraspectra inin thethe syntheticsyntheticPd Pd99AgAg22Bi2S44 andand in in the the natural natural material. material.

Raman spectra were obtained using a LABRAM (ISA Jobin Yvon) instrumentinstrument installed at the University of Leoben, Austria. Austria. A A frequency-doubled frequency-doubled 100 100 mW mW Nd:YAG Nd:YAG laser laser with with an an excitation excitation of of a awavelength wavelength of λ of = λ532.6= 532.6 nm was nm used. was used.The obtained The obtained Raman spectra Raman of spectra natural ofand natural synthetic and Pd synthetic9Ag2Bi2S4 show four discernible absorption bands at the following values: 122, 309, 362, and 483 cm−1 (see Figure 8). Pd9Ag2Bi2S4 show four discernible absorption bands at the following values: 122, 309, 362, and 483 cmThe−1 EBSD(see Figure study,8 ).Raman spectra, chemical identity and optical properties confirmed the identity of theThe natural EBSD and study, synthetic Raman materials spectra, chemical and thereby identity legitimise and optical the use properties of the synthetic conﬁrmed phase the identity for the ofcomplete the natural characterization and synthetic of materialsthalhammerite. and thereby legitimise the use of the synthetic phase for the complete characterization of thalhammerite. Author Contributions: All the authors (A.V., F.L., S.F.S., V.V.K., C.J.S., J.P., F.Z., G.G. and R.B.) discussed the Authorobtained Contributions: results, evaluatedAll thethe authorsdata and (A.V., wrote F.L., the S.F.S., article V.V.K., together. C.J.S., A.V. J.P., designed F.Z., G.G. the and article R.B.) and discussed conceived the obtainedexperiments; results, S.F.S. evaluated provided the the data samples and wrote and the geological article together. background; A.V. designed F.L., V.V.K., the article J.P. andobtained conceived the experiments;crystallographic S.F.S. data; provided C.J.S. theprovided samples optical and geological properties; background; F.Z., G.G. F.L.,and V.V.K.,R.B. studied J.P. obtained thalhammerite the crystallographic by Raman data;and evaluated C.J.S. provided the chemical optical data. properties; All the F.Z., authors G.G. revised and R.B. and studied edited thalhammerite the manuscript. by Raman and evaluated the chemical data. All the authors revised and edited the manuscript. Funding: The work was supported by the Grant Agency of the Czech Republic (project no. 18-15390S to A.V.), Funding: The work was supported by the Grant Agency of the Czech Republic (project no. 18-15390S to A.V.),through through an internal an internal project project331400 331400from the from Czech the Geologic Czech Geologicalal Survey, the Survey, Russian the Foundation Russian Foundation for Basic Research for Basic Research(project RFBR (project 18-05-70073), RFBR 18-05-70073), and C.J.S. and C.J.S.acknowledges acknowledges Natural Natural Environment Environment Research Research Council, Council, grant NE/M010848/1, Tellurium Tellurium and and Se Seleniumlenium Cycling Cycling and and Supply. Supply.

Acknowledgments: The authors acknowledge Ulf Hålenius, Chai Chairmanrman of the CNMNC and its members for helpful comments on the submitted data. The authors are grateful to Zuzana Korbelová (Institute of Geology helpful comments on the submitted data. The authors are grateful to Zuzana Korbelová (Institute of Geology AS AS CR, v.v.i.) for carrying out the electron microprobe analyses. We thank two anonymous reviewers and the EditorialCR, v.v.i.) Board for carrying members, out for the their electron comments microprobe and improvements. analyses. We thank two anonymous reviewers and the Editorial Board members, for their comments and improvements. Conﬂicts of Interest: The authors declare no conﬂict of interest. Conflicts of Interest: The authors declare no conflict of interest.

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