Tetrahedrite-(Hg), a new 'old' member of the tetrahedrite group

Tetrahedrite-(Hg), Cu6(Cu4Hg2)Sb4S13, has been approved as a new mineral species using samples from Buca della Vena mine (hereafter BdV), Italy, Jedová hora (Jh), Czech Republic and RoŽÅ 1/2ava (R), Slovakia. It occurs as anhedral grains or as tetrahedral crystals, black in colour, with metallic lustre. At BdV it is associated with cinnabar and chalcostibite in dolomite veins. At Jh, tetrahedrite-(Hg) is associated with baryte and chalcopyrite in quartz-siderite-dolomite veins; at R it is associated with quartz in siderite-quartz veins. Tetrahedrite-(Hg) is isotropic, greyish-white in colour, with creamy tints. Minimum and maximum reflectance data for Commission on Ore Mineralogy wavelengths in air (BdV sample), R in %) are 32.5 at 420 nm; 32.9 at 546 nm; 33.2 at 589 nm; and 30.9 at 650 nm. Chemical formulae of the samples studied, recalculated on the basis of 4 (As + Sb + Bi) atoms per formula unit, are: (Cu9.44Ag0.07)Σ9.51(Hg1.64Zn0.36Fe0.06)Σ2.06Sb4(S12.69Se0.01)Σ12.70 (BdV), Cu9.69(Hg1.75Fe0.25Zn0.06)Σ2.06(Sb3.94As0.06)S12.87 (Jh) and (Cu9.76Ag0.04) Σ9.80(Hg1.83Fe0.15Zn0.10)Σ2.08(Sb3.17As0.58Bi0.25)S13.01 (R). Tetrahedrite-(Hg) is cubic, I3m, with a = 10.5057(8) Å, V = 1159.5(3) Å3 and Z = 2 (BdV). Unit-cell parameters for the other two samples are a = 10.4939(1) Å and V = 1155.61(5) Å3 (Jh) and a = 10.4725(1) Å and V = 1148.55(6) Å3 (R). The crystal structure of tetrahedrite-(Hg) has been refined by single-crystal X-ray diffraction data to a final R1 = 0.019 on the basis of 335 reflections with Fo > 4σ(Fo) and 20 refined parameters. Tetrahedrite-(Hg) is isotypic with other members of the tetrahedrite group. Mercury is hosted at the tetrahedrally coordinated M(1) site, along with minor Zn and Fe. The occurrence of Hg at this position agrees both with the relatively large M(1)-S(1) bond distance (2.393 Å) and the refined site scattering. Previous occurrences of Hg-rich tetrahedrite and tetrahedrite-(Hg) are reviewed, and its relations with other Hg sulfosalts are discussed

Dussertite BaFe3+3(AsO4)2(OH)5 : a Raman spectroscopic study of a hydroxy-arsenate mineral

The mineral dussertite, a hydroxy-arsenate mineral of formula BaFe3+3(AsO4)2(OH)5, has been studied by Raman complimented with infrared spectroscopy. The spectra of three minerals from different origins were investigated and proved quite similar, although some minor differences were observed. In the Raman spectra of Czech dussertite, four bands are observed in the 800 to 950 cm-1 region. The bands are assigned as follows: the band at 902 cm-1 is assigned to the (AsO4)3- ν3 antisymmetric stretching mode, at 870 cm-1 to the (AsO4)3- ν1 symmetric stretching mode, and both at 859 cm-1 and 825 cm-1 to the As-OM2+/3+ stretching modes/and or hydroxyls bending modes. Raman bands at 372 and 409 cm-1 are attributed to the ν2 (AsO4)3- bending mode and the two bands at 429 and 474 cm-1 are assigned to the ν4 (AsO4)3- bending mode. An intense band at 3446 cm-1 in the infrared spectrum and a complex set of bands centred upon 3453 cm-1 in the Raman spectrum are attributed to the stretching vibrations of the hydrogen bonded (OH)- units and/or water units in the mineral structure. The broad infrared band at 3223 cm-1 is assigned to the vibrations of hydrogen bonded water molecules. Raman spectroscopy identified Raman bands attributable to (AsO4)3- and (AsO3OH)2- units

Fluorarrojadite-(BaNa), BaNa4CaFe13Al(PO4)11(PO3OH)F2, a new member of the arrojadite group from Gemerská Poloma, Slovakia

The new mineral fluorarrojadite-(BaNa), ideally BaNa4CaFe13Al(PO4)11(PO3OH)F2 was found on the dump of of Elisabeth adit near Gemersk\ue1 Poloma, Slovakia. It occurs in hydrothermal quartz veins intersecting highly fractionated, topaz-zinnwaldite S-type leucogranite. Fluorarrojadite-(BaNa) is associated with fluorapatite, \u201cfluordickinsonite-(BaNa)\u201d, triplite, viitaniemiite and minor amounts of other minerals. It forms fine grained irregular aggregates up to 4 x 2 cm, which consists of individual anhedral grains up to 0.01 mm in size. It has a yellowish-brown to greenish-yellow colour, very pale yellow streak, a vitreous to greasy lustre. Mohs hardness is about 4\ubd to 5. The fracture is irregular and the tenacity is brittle. The measured density is 3.61(2) g\ub7cm-3 28 and calculated density is 3.650 g\ub7cm-3 29 . Fluorarrojadite-(BaNa) is biaxial (+) and nonpleochroic. The calculated refractive index based on empirical formula is 1.674. The empirical formula (based on 47 O and 3 (OH+F) apfu) is A1(Ba0.65K0.35)\u3a31.00 A2Na0.35 B1(Na0.54Fe0.46)\u3a31.00 B2Na0.54 Ca(Ca0.74Sr0.20Pb0.02Ba0.04)\u3a31.00Na2Na3 32 Na0.46M(Fe7.16Mn5.17Li0.37Mg0.12Sc0.08Zn0.06Ga0.02Ti0.02)\u3a313.00Al1.02P11O44PO3.46(OH)0.54 W 33 (F1.54OH0.46).Fluorarrojadite-(BaNa) is monoclinic, space group Cc, a = 16.563(1) \uc5, b = 10.0476(6) \uc5, c = 24.669(1) \uc5, \u3b2 = 105.452(4)\ub0, V = 3957.5(4) \uc53 and Z = 4. The seven strongest reflections in the powder X-ray diffraction pattern are [dobs in \uc5, (I), hkl]: 3.412, (21), 116; 3.224, (37), 206; 3.040, (100), 42-4; 2.8499, (22), 33-2; 2.7135, (56), 226; 2.5563, (33), 028 and 424; 2.5117, (23), 040. The new mineral is named according to the actual nomenclature scheme of arrojadite group minerals, which was approved by the CNMNC IMA. In fluorarrojadite-(BaNa) Fe2+ 40 is a dominant cation at the M site (so the root-name is arrojadite) and two suffixes are added to the root-name according to the dominant cation of the dominant valence state at the A1 (Ba2+) and B1 sites (Na+). A prefix fluor is added to the root-name as F- 42 is dominant over (OH)- 43 at the W site

A vibrational spectroscopic study of hydrated Fe3+ hydroxyl-sulfates; polymorphic minerals butlerite and parabutlerite

Raman and infrared spectra of two polymorphous minerals with the chemical formula Fe3+(SO4)(OH)•2H2O, monoclinic butlerite and orthorhombic parabutlerite, are studied and the spectra assigned. Observed bands are attributed to the (SO4)2- stretching and bending vibrations, hydrogen bonded water molecules, stretching and bending vibrations of hydroxyl ions, water librational modes, Fe-O and Fe-OH stretching vibrations, Fe-OH bending vibrations and lattice vibrations. The O-H...O hydrogen bond lengths in the structures of both minerals are calculated from the wavenumbers of the stretching vibrations. One symmetrically distinct (SO4)2- unit in the structure of butlerite and two symmetrically distinct (SO4)2- units in the structure of parabutlerite are inferred from the Raman and infrared spectra. This conclusion agrees with the published crystal structures of both mineral phases

The crystal structures and mechanical properties of the uranyl carbonate minerals roubaultite, fontanite, sharpite, widenmannite, grimselite and čejkaite

25 pags., 17 figs., 5 tabs.The research involving the crystal structures and properties of uranyl carbonate minerals is essential in actinide environmental chemistry due to the fundamental role played by these minerals in the migration of actinides from uranium deposits and nuclear waste repositories and in the investigation of accidental site contaminations. In this work, the crystal structure, hydrogen bonding network, X-ray diffraction pattern and mechanical properties of six important uranyl carbonate minerals, roubaultite (Cu2[(UO2)3(CO3)2(OH)2]·4H2O), fontanite (Ca[(UO2)3(CO3)2(OH)2]·6H2O), sharpite (Ca[(UO2)3(CO3)4(OH)2]·3H2O), widenmannite (Pb2[(UO2)(CO3)2(OH)2]), grimselite (K3Na[(UO2)(CO3)3]·H2O) and čejkaite (Na4[(UO2)(CO3)3]), are investigated using first principles solid-state methods based in density functional theory. The determination of the positions of the hydrogen atoms in the unit cells of fontanite, sharpite and grimselite minerals, defining the hydrogen bonding network in their crystal structures, has not been feasible so far due to the low quality of their experimental X-ray diffraction patterns. The full crystal structures of these minerals are obtained here and their hydrogen bonding networks are studied in detail. Furthermore, the experimental structures of roubaultite, widenmannite and čejkaite, obtained by refinement from X-ray diffraction data, are confirmed. In the six cases, the computed unit-cell parameters and the associated geometrical variables are in excellent agreement with the available experimental information. Furthermore, the X-ray diffraction patterns computed from the optimized structures are in satisfactory agreement with their experimental counterparts. The knowledge of the full crystal structures, being extraordinarily relevant for many scientific fields, is also extremely interesting because it opens the possibility of determining their physico-chemical properties using the first principles methodology. The measurement of these properties under safe conditions is very expensive and complicated due to the radiotoxicity of these minerals. In this paper, a large set of relevant mechanical properties of these minerals are determined including their bulk, shear and Young moduli, the Poisson's ratio, ductility, hardness and anisotropy indices and bulk modulus pressure derivatives. These properties have not been measured so far and, therefore, are predicted here. Four of these minerals, roubaultite, fontanite, sharpite and widemmannite, are highly anisotropic and exhibit negative mechanical phenomena under the effect of small external pressures. This journal isThe supercomputer time provided by the CTI-CSIC center is greatly acknowledged. This work has been carried out in the context of a CSIC–CIEMAT collaboration agreement: “Caracterización experimental y teórica de fases secundarias y óxidos de uranio formados en condiciones de almacenamiento de combustible nuclear”. JP acknowledges the support of the Czech Science Foundation through the project GACR 20- 11949S. JS was supported by the Ministry of Culture of the Czech Republic (long-term project DKRVO 2019–2023/1.II.b; National Museum, 00023272)