Radvaniceite, GeS 2 , a New Germanium Sulphide, from the Kateˇrina Mine, Radvanice near Trutnov, Czech Republic

: The new mineral radvaniceite, GeS 2 , was found on the burning coal mine dump of the abandoned Kateˇrina coal mine at Radvanice, near Trutnov, northern Bohemia, Czech Republic. It occurs as aggregates resembling cotton tufts up to 5 mm in size; they are composed of acicular crystals up to fibres about 1–5 µ m thick and up to 3 mm in length. Individual fibres are distorted and partly resemble bent wires nucleated on rock fragments or on black, crumbly ash, in association with minerals of solid solutions of Bi-Sb and stangersite, herzenbergite, and greenockite. Radvaniceite was also observed as irregular grains in a range of 10–50 µ m in size, forming part of earlier multicomponent aggregates upon which the above-described crystals grow. These aggregates are formed, in addition to radvaniceite, by minerals of Bi-Sb, Bi 2 S 3 -Sb 2 S 3 and Bi 2 S 3 -Bi 2 Se 3 solid solutions, Bi 3 S 2 , Bi-sulpho/seleno/tellurides, tellurium, unnamed PbGeS 3 , Cd 4 GeS 6 , GeAsS, Sn 5 Sb 3 S 7 , stangersite, greenockite, cadmoindite, herzen-bergite, teallite, and Sn- and/or Se-bearing galena. Radvaniceite is formed under reducing conditions by direct crystallization from hot gasses (250–350 ◦ C) containing Cl and F at a depth of 30–60 cm under the surface of a burning coal mine dump; the mine dump fire started spontaneously, and no anthropogenic material was deposited there. Acicular crystals up to fibres of radvaniceite are elastic to flexible; are white to yellowish grey in colour, with white streaks; are translucent in transmitted light; and have vitreous to adamantine lustre. Cleavage and fracture were not observed. The calculated density is 3.05 corner-sharing tetrahedral chains, which are connected by corner-sharing tetrahedra in a three-dimensional structure. We named the mineral after its type locality, Radvanice, one of the past centres of coal mining in the Czech limb of the Intra-Sudetic Basin. This mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (number 2021-052).

As mentioned above, two morphological types of radvaniceite were observed in the studied material. The first type is represented by aggregates resembling cotton tufts up to 5 mm in size ( Figure 1); they are composed of acicular crystals up to fibres about 1-5 µm thick and up to 3 mm in length. Individual fibres are distorted and partly resemble bent wires ( Figure 2). The second type forms irregular grains 10-50 µm in size as a part of previously formed multicomponent aggregates. Radvaniceite is white to yellowish grey in colour, with white streaks. The mineral is translucent in transmitted light and has vitreous to adamantine lustre. Cleavage and fracture were not observed, the tenacity is elastic to flexible. The calculated density (Z = 12) is 3.05 and 2.99 g·cm −3 for empirical and ideal formulae, respectively. Radvaniceite is transparent under a microscope, with a very weak pleochroism (from colourless to pale greenish yellow). The index of refraction is >1.8; other properties cannot be determined due to fine nature of the sample.
In reflected light radvaniceite is light grey; bireflectance and pleochroism were not observed due to abundant white to grey internal reflections. Anisotropy in crossed polars is distinct, with grey rotation tints. Reflectance percentages (air) for the four COM wavelengths (R min and R max , %) for radvaniceite are: 15.4-18.8 (470 nm), 16.1-20.4 (546 nm), 16.4-20.8 (589 nm), and 6.9-20.9 (650 nm). The full set of reflectance values (spectrophotometer MSP400 Tidas coupled to a Leica microscope, objective 100×, WTiC standard Zeiss 370 in air) are given in Table 1 and plotted in Figure 3.

Chemical Composition
The holotype sample of radvaniceite was analysed using a JEOL Superprobe 733 electron microprobe operated in the wavelength-dispersive mode with an accelerating voltage of 20 kV, a specimen current of 20 nA, and a beam diameter of 1-2 μm. The following lines and standards were used: Kα: chalcopyrite (Fe, S); Lα: Bi (Bi), CdS (Cd), Cu3AsS4 (As), Ge (Ge), Sb2Se3 (Sb, Se), Sn (Sn); Mα: PbS (Pb). The raw intensities were converted into concentrations automatically, using the online ZAF correction program supplied by JEOL. Detection limits were close to 0.02-0.05 wt. %. Absence of H2O and CO2 was confirmed by Raman spectroscopy. Chemical analyses of other samples were performed using a Cameca SX100 electron microprobe operating in wavelength-dispersive mode (15 kV, 10 nA, and 0.7 μm wide beam). The following standards and X-ray lines were used to minimise line overlaps: Ge (GeLα), Bi (BiMβ), CdTe (CdLα), FeS2 (FeKα, SKα), NiAs (AsLβ), PbS (PbMα), PbSe (SeLβ), PbTe (TeLα), and Sb2S3 (SbLα). Peak counting times were 20 s for all elements, and one half of the peak time for each background. Some elements, such as Cd, Fe, As, Pb, Te, and Sb, were found to be below the detection limits (0.02-0.05 wt. %). Raw intensities were converted to the concentrations of elements using the automatic "PAP" [28] matrix-correction procedure.

Chemical Composition
The holotype sample of radvaniceite was analysed using a JEOL Superprobe 733 electron microprobe operated in the wavelength-dispersive mode with an accelerating voltage of 20 kV, a specimen current of 20 nA, and a beam diameter of 1-2 µm. The following lines and standards were used: Kα: chalcopyrite (Fe, S); Lα: Bi (Bi), CdS (Cd), Cu 3 AsS 4 (As), Ge (Ge), Sb 2 Se 3 (Sb, Se), Sn (Sn); Mα: PbS (Pb). The raw intensities were converted into concentrations automatically, using the online ZAF correction program supplied by JEOL. Detection limits were close to 0.02-0.05 wt. %. Absence of H 2 O and CO 2 was confirmed by Raman spectroscopy. Chemical analyses of other samples were performed using a Cameca SX100 electron microprobe operating in wavelength-dispersive mode (15 kV, 10 nA, and 0.7 µm wide beam). The following standards and X-ray lines were used to minimise line overlaps: Ge (GeLα), Bi (BiMβ), CdTe (CdLα), FeS 2 (FeKα, SKα), NiAs (AsLβ), PbS (PbMα), PbSe (SeLβ), PbTe (TeLα), and Sb 2 S 3 (SbLα). Peak counting times were 20 s for all elements, and one half of the peak time for each background. Some elements, such as Cd, Fe, As, Pb, Te, and Sb, were found to be below the detection limits (0.02-0.05 wt. %). Raw intensities were converted to the concentrations of elements using the automatic "PAP" [28] matrix-correction procedure.
Chemical composition of radvaniceite from the holotype sample (Table 2) corresponds to the ideal formula GeS 2 with only minor contents of Sn, Sb, As, and Bi up to 0.01 apfu, and Pb up to 0.003 apfu, respectively. The extent of SeS -1 substitution in anions of this sample is limited to 0.06 apfu Se (Figure 4). The empirical formula calculated from the mean of 12 point analyses on the basis of 3 apfu is as follows: (Ge 0.99 Bi 0.01 ) Σ1.00 (S 1.97 Se 0.03 ) Σ2.00 . The ideal formula, GeS 2 , requires Ge 53.10, S 46.90, total 100 wt. %. The representative analyses for the holotype and other samples are given in Table 3. The selenium contents of other samples were detected in the range 0.09-0.10 apfu (Figure 4). Chemical composition of radvaniceite from the holotype sample (Table 2) corresponds to the ideal formula GeS2 with only minor contents of Sn, Sb, As, and Bi up to 0.01 apfu, and Pb up to 0.003 apfu, respectively. The extent of SeS-1 substitution in anions of this sample is limited to 0.06 apfu Se (Figure 4). The empirical formula calculated from the mean of 12 point analyses on the basis of 3 apfu is as follows: (Ge0.99Bi0.01)Σ1.00(S1.97Se0.03)Σ2.00. The ideal formula, GeS2, requires Ge 53.10, S 46.90, total 100 wt. %. The representative analyses for the holotype and other samples are given in Table 3. The selenium contents of other samples were detected in the range 0.09-0.10 apfu (Figure 4).      Coefficients of empirical formula calculated on the basis of 3 apfu.

Raman Spectroscopy
The Raman spectra of radvaniceite were collected in the range of 36-1800 cm −1 using a DXR dispersive Raman Spectrometer (Thermo Scientific, Waltham, MA, USA) mounted on a confocal Olympus microscope. The Raman signal was excited by an unpolarised green 532 nm solid state, diode-pumped laser, and detected by a CCD detector. The experimental parameters were: 100× objective, 10 s exposure time, 100 exposures, 50 µm pinhole spectrograph aperture and 1 mW laser power level. Eventual thermal damage of the measured points was excluded by visual inspection of excited surfaces after measurement, by observation of possible decay of spectral features at the start of excitation, and by checking for thermal downshift of Raman lines. The instrument was set up by a software-controlled calibration procedure using multiple neon emission lines (wavelength calibration), multiple polystyrene Raman bands (laser frequency calibration) and standardised white-light sources (intensity calibration). Spectral manipulations were performed using Omnic 9 software (Thermo Scientific).

Powder X-Ray Diffraction and Crystal Structure
Attempts to obtain single-crystal X-ray data of radvaniceite were unsuccessful due to the nature of the studied material, which is formed by bent fibres (Figure 2). The X-ray powder diffraction data for radvaniceite (Table 4) were recorded at room temperature using a Bruker D8 Advance diffractometer equipped with a solid-state LynxEye detector and secondary monochromator producing CuKα radiation, housed at the Department of Mineralogy and Petrology, National Museum, Prague, Czech Republic. The instrument was operated at 40 kV and 40 mA. In order to minimise the background, the powder samples were placed (without any liquid) on the surface of a flat silicon wafer. The powder pattern was collected in the Bragg-Brentano geometry in the range 3-70° 2θ, step 0.01° and counting time of 20 s per step (total duration of the experiment was c. 30 h). The positions and intensities of diffractions were found and refined using the Pearson VII profile-shape function of the ZDS program package [35].

Powder X-ray Diffraction and Crystal Structure
Attempts to obtain single-crystal X-ray data of radvaniceite were unsuccessful due to the nature of the studied material, which is formed by bent fibres (Figure 2).
The X-ray powder diffraction data for radvaniceite (Table 4) were recorded at room temperature using a Bruker D8 Advance diffractometer equipped with a solid-state Lynx-Eye detector and secondary monochromator producing CuKα radiation, housed at the Department of Mineralogy and Petrology, National Museum, Prague, Czech Republic. The instrument was operated at 40 kV and 40 mA. In order to minimise the background, the powder samples were placed (without any liquid) on the surface of a flat silicon wafer. The powder pattern was collected in the Bragg-Brentano geometry in the range 3-70 • 2θ, step 0.01 • and counting time of 20 s per step (total duration of the experiment was c. 30 h). The positions and intensities of diffractions were found and refined using the Pearson VII profile-shape function of the ZDS program package [35].              Icalc. *-intensities were calculated using the software PowderCell 2.3 [36] on the basis of the crystal structure of β-GeS2 [6].
Crystal structure of low-temperature β-GeS2 was published by Zachariasen [7] in orthorhombic symmetry (space group Fdd2) with a = 11.60 (5), b = 22.34 (10), c = 6.86 (3) Å; later it was re-determined by Dittmar and Schäfer [6]. In contrast to an earlier determination, they found that it crystallises in the monoclinic space group Pc with unit-cell parameters a = 6.875 (5), b = 22.55 (1), c = 6.809 (5) Å and β = 120.45 (5)°. The crystal structure of radvaniceite is based on corner-sharing GeS4 tetrahedra. In this structure, a system of chains of corner-sharing GeS4 tetrahedra running along [001] and [010] can be visualised. However, these chains are interconnected by corner-sharing of GeS4 tetrahedra, forming a framework structure ( Figure 6). From a crystallographic point of view, the GeS4 corner-sharing framework in the radvaniceite crystal structure shows certain similarities to those found in tetrahedral networks of common SiO2 polymorphs. The main difference lies in the angles of Ge-S-Ge and Si-O-Si bonds connecting two adjacent tetrahedra. In β-GeS2, an analogue of radvaniceite, this angle varies from 99.8 to 102.8° whereas in, e.g., α-quartz it has a value of 144° [38]. Another remarkable feature is that the GeS4 tetrahedra in the radvaniceite structure are more distorted than corresponding SiO4 tetrahedra in the α-quartz structure. Whereas the value of quadratic elongation for SiO4 tetrahedra in  Icalc. *-intensities were calculated using the software PowderCell structure of β-GeS2 [6].
Crystal structure of low-temperature β-GeS2 was pu orthorhombic symmetry (space group Fdd2) with a = 11.60 later it was re-determined by Dittmar and Schäfer [6]. In nation, they found that it crystallises in the monoclinic sp rameters a = 6.875 (5), b = 22.55 (1), c = 6.809 (5) Å and β = 1 of radvaniceite is based on corner-sharing GeS4 tetrahedra chains of corner-sharing GeS4 tetrahedra running along [00 However, these chains are interconnected by corner-shari a framework structure (Figure 6). From a crystallographi ner-sharing framework in the radvaniceite crystal structu those found in tetrahedral networks of common SiO2 pol lies in the angles of Ge-S-Ge and Si-O-Si bonds connectin β-GeS2, an analogue of radvaniceite, this angle varies from α-quartz it has a value of 144° [38]. Another remarkable fea in the radvaniceite structure are more distorted than corres α-quartz structure. Whereas the value of quadratic elon   Icalc. *-intensities were calculated using the software PowderCell structure of β-GeS2 [6].
Crystal structure of low-temperature β-GeS2 was pu orthorhombic symmetry (space group Fdd2) with a = 11.60 later it was re-determined by Dittmar and Schäfer [6]. In nation, they found that it crystallises in the monoclinic sp rameters a = 6.875 (5)   Icalc. *-intensities were calculated using the software PowderCell 2.3 [36] on the basis of the crystal structure of β-GeS2 [6].
However, these chains are interconnected by corner-sharing of GeS4 tetrahedra, forming a framework structure (Figure 6). From a crystallographic point of view, the GeS4 corner-sharing framework in the radvaniceite crystal structure shows certain similarities to those found in tetrahedral networks of common SiO2 polymorphs. The main difference lies in the angles of Ge-S-Ge and Si-O-Si bonds connecting two adjacent tetrahedra. In β-GeS2, an analogue of radvaniceite, this angle varies from 99.8 to 102.8° whereas in, e.g., α-quartz it has a value of 144° [38]. Another remarkable feature is that the GeS4 tetrahedra in the radvaniceite structure are more distorted than corresponding SiO4 tetrahedra in the   Icalc. *-intensities were calculated using the software PowderCell structure of β-GeS2 [6].
Crystal structure of low-temperature β-GeS2 was pu orthorhombic symmetry (space group Fdd2) with a = 11.60 later it was re-determined by Dittmar and Schäfer [6]. In nation, they found that it crystallises in the monoclinic sp rameters a = 6.875 (5)    Icalc. *-intensities were calculated using the software PowderCell 2.3 [36] on the basis of the crystal structure of β-GeS2 [6].
However, these chains are interconnected by corner-sharing of GeS4 tetrahedra, forming a framework structure (Figure 6). From a crystallographic point of view, the GeS4 corner-sharing framework in the radvaniceite crystal structure shows certain similarities to those found in tetrahedral networks of common SiO2 polymorphs. The main difference lies in the angles of Ge-S-Ge and Si-O-Si bonds connecting two adjacent tetrahedra. In β-GeS2, an analogue of radvaniceite, this angle varies from 99.8 to 102.8° whereas in, e.g., α-quartz it has a value of 144° [38]. Another remarkable feature is that the GeS4 tetrahedra in the radvaniceite structure are more distorted than corresponding SiO4 tetrahedra in the α-quartz structure. Whereas the value of quadratic elongation for SiO4 tetrahedra in  Table 4. X-ray powder diffraction data (d in Å) for radvaniceite ported in bold. Icalc. *-intensities were calculated using the software PowderCell structure of β-GeS2 [6].

Imeas
Crystal structure of low-temperature β-GeS2 was pu orthorhombic symmetry (space group Fdd2) with a = 11.60 later it was re-determined by Dittmar and Schäfer [6]. In nation, they found that it crystallises in the monoclinic sp rameters a = 6.875 (5) Table 4. X-ray powder diffraction data (d in Å) for radvaniceite, the strongest diffractions are reported in bold. Icalc. *-intensities were calculated using the software PowderCell 2.3 [36] on the basis of the crystal structure of β-GeS2 [6].
However, these chains are interconnected by corner-sharing of GeS4 tetrahedra, forming a framework structure (Figure 6). From a crystallographic point of view, the GeS4 corner-sharing framework in the radvaniceite crystal structure shows certain similarities to those found in tetrahedral networks of common SiO2 polymorphs. The main difference lies in the angles of Ge-S-Ge and Si-O-Si bonds connecting two adjacent tetrahedra. In β-GeS2, an analogue of radvaniceite, this angle varies from 99.8 to 102.8° whereas in, e.g., α-quartz it has a value of 144° [38]. Another remarkable feature is that the GeS4 tetrahedra in the radvaniceite structure are more distorted than corresponding SiO4 tetrahedra in the   Icalc. *-intensities were calculated using the software PowderCell structure of β-GeS2 [6].
Crystal structure of low-temperature β-GeS2 was pu orthorhombic symmetry (space group Fdd2) with a = 11.60 later it was re-determined by Dittmar and Schäfer [6]. In nation, they found that it crystallises in the monoclinic sp rameters a = 6.875 (5), b = 22.55 (1), c = 6.809 (5) Å and β = 1 of radvaniceite is based on corner-sharing GeS4 tetrahedra chains of corner-sharing GeS4 tetrahedra running along [00 However, these chains are interconnected by corner-shari a framework structure (Figure 6). From a crystallographi ner-sharing framework in the radvaniceite crystal structu those found in tetrahedral networks of common SiO2 pol lies in the angles of Ge-S-Ge and Si-O-Si bonds connectin β-GeS2, an analogue of radvaniceite, this angle varies from α-quartz it has a value of 144° [38]. Another remarkable fea in the radvaniceite structure are more distorted than corres α-quartz structure. Whereas the value of quadratic elon   Icalc. *-intensities were calculated using the software PowderCell 2.3 [36] on the basis of the crystal structure of β-GeS2 [6].
However, these chains are interconnected by corner-sharing of GeS4 tetrahedra, forming a framework structure (Figure 6). From a crystallographic point of view, the GeS4 corner-sharing framework in the radvaniceite crystal structure shows certain similarities to those found in tetrahedral networks of common SiO2 polymorphs. The main difference lies in the angles of Ge-S-Ge and Si-O-Si bonds connecting two adjacent tetrahedra. In β-GeS2, an analogue of radvaniceite, this angle varies from 99.8 to 102.8° whereas in, e.g., α-quartz it has a value of 144° [38]. Another remarkable feature is that the GeS4 tetrahedra in the radvaniceite structure are more distorted than corresponding SiO4 tetrahedra in the α-quartz structure. Whereas the value of quadratic elongation for SiO4 tetrahedra in   Icalc. *-intensities were calculated using the software PowderCell structure of β-GeS2 [6].
Crystal structure of low-temperature β-GeS2 was pu orthorhombic symmetry (space group Fdd2) with a = 11.60 later it was re-determined by Dittmar and Schäfer [6]. In nation, they found that it crystallises in the monoclinic sp rameters a = 6.875 (5), b = 22.55 (1), c = 6.809 (5) Å and β = 1 of radvaniceite is based on corner-sharing GeS4 tetrahedra chains of corner-sharing GeS4 tetrahedra running along [00 However, these chains are interconnected by corner-shari a framework structure (Figure 6). From a crystallographi ner-sharing framework in the radvaniceite crystal structu those found in tetrahedral networks of common SiO2 pol lies in the angles of Ge-S-Ge and Si-O-Si bonds connectin β-GeS2, an analogue of radvaniceite, this angle varies from α-quartz it has a value of 144° [38]. Another remarkable fea in the radvaniceite structure are more distorted than corres α-quartz structure. Whereas the value of quadratic elon The PXRD data of radvaniceite agree well with the theoretical pattern calculated by the PowderCell 2.3 program [36] from the crystal structure information published by Dittmar and Schäfer [6] for β-GeS 2 ; this calculated pattern was also used for indexing of experimental data. The following unit-cell parameters, refined by the least-squares program of Burnham [37]: a = 6.8831 (12), b = 22.501(3), c = 6.8081(11) Å, β = 120.365(9) • , V = 909.8(4) Å 3 and Z = 12, agree very well with data published by Dittmar and Schäfer [6] for β-GeS 2 .
Crystal structure of low-temperature β-GeS 2 was published by Zachariasen [7] in orthorhombic symmetry (space group Fdd2) with a = 11.60 (5), b = 22.34 (10), c = 6.86 (3) Å; later it was re-determined by Dittmar and Schäfer [6]. In contrast to an earlier determination, they found that it crystallises in the monoclinic space group Pc with unit-cell parameters a = 6.875 (5), b = 22.55 (1), c = 6.809 (5) Å and β = 120.45 (5) • . The crystal structure of radvaniceite is based on corner-sharing GeS 4 tetrahedra. In this structure, a system of chains of corner-sharing GeS 4 tetrahedra running along [001] and [010] can be visualised. However, these chains are interconnected by corner-sharing of GeS 4 tetrahedra, forming a framework structure (Figure 6). From a crystallographic point of view, the GeS 4 corner-sharing framework in the radvaniceite crystal structure shows certain similarities to those found in tetrahedral networks of common SiO 2 polymorphs. The main difference lies in the angles of Ge-S-Ge and Si-O-Si bonds connecting two adjacent tetrahedra. In β-GeS 2 , an analogue of radvaniceite, this angle varies from 99.8 to 102.8 • whereas in, e.g., α-quartz it has a value of 144 • [38]. Another remarkable feature is that the GeS 4 tetrahedra in the radvaniceite structure are more distorted than corresponding SiO 4 tetrahedra in the α-quartz structure. Whereas the value of quadratic elongation for SiO 4 tetrahedra in α-quartz is 1.0002, values for GeS 4 tetrahedra in the radvaniceite structure fall within the range of 1.008-1.0099.
Minerals 2022, 12, x FOR PEER REVIEW 10 of 12 α-quartz is 1.0002, values for GeS4 tetrahedra in the radvaniceite structure fall within the range of 1.008-1.0099.

Note on the Origin of Radvaniceite
The element germanium is compatible with rock-forming silicates, where it substitutes for Si due to its similar ionic radius (0.53 and 0.40 Å, for Si and Ge, respectively) and its possession of the same charge. The bulk Ge content in common rocks varies from ~0.1 to ~2.5 ppm [39,40]. However, Ge can accumulate substantially in some sphalerite deposits, coal, organic matter, and petrified wood [39,40]. As coal from the Radvanice area is substantially enriched in Ge (average 192 g/t, maximum 940 g/t in ash [41]), its spontaneous combustion in the Radvanice dump mobilised Ge and other elements (Sn, Sb, As, Bi, etc.) into escaping hot gases using Cl as a transporting agent (e.g., Laufek et al. [23]) together with omnipresent S and NH3. Radvaniceite locally crystallised when the temperature of such mineralised gasses dropped below the stability of the Ge gaseous complexes.