Ferdowsiite from the Monte Arsiccio mine, Apuan Alps, Tuscany (Italy): occurrence and crystal structure

A new finding of ferdowsiite, ideally Ag8Sb5As3S16, from the Monte Arsiccio mine, Apuan Alps, Tuscany (Italy) is reported. Ferdowsiite occurs as black euhedral crystals, up to 0.3 mm in size, associated with arsiccioite, boscardinite, and chabournéite in small vugs of baryte + dolomite veins embedded in the pyrite-rich metadolostone close to the contact with the baryte + pyrite ore body. Electron microprobe data gave (wt% - mean of nine spot analyses): Ag 39.03(36), Pb 0.24(3), As 10.63(18), Sb 26.57(9), S 23.71(14), Cl 0.04(1), total 100.22(41). On the basis of ΣMe = 16 apfu, the chemical formula is Ag8.01(5)Pb0.03(1) Sb4.83(2)As3.14(4)S16.36(15)Cl0.03(1). The crystal structure of ferdowsiite has been refined in the space group P21/n, with unit-cell parameters a = 8.6573(4), b = 5.7896(3), c = 13.7866(7) Å, β = 96.122(2)°, V = 687.08(6) Å3, Z = 1. The R1 factor converged to 0.024 on the basis of 1898 reflections with Fo > 4σ(Fo) and 75 parameters

Lead-antimony sulfosalts from Tuscany (Italy). XXIII. Andreadiniite, CuAg7HgPb7Sb24S48, a new oversubstituted (Cu,Hg)-rich member of the andorite homeotypic series from the Monte Arsiccio mine, Apuan Alps

The new mineral species andreadiniite, CuAg7HgPb7Sb24S48, was discovered in a quartz vein embedded in metadolostone from the Sant'Olga tunnel, Monte Arsiccio mine, Stazzema, Apuan Alps, Tuscany, Italy. It occurs as black anhedral grains, up to some mm in size, with a metallic luster, associated with sphalerite and stibnite. Under the ore microscope, andreadiniite is white, with a slightly yellow-bronze tint. Pleochroism was not observed. Anisotropism is weak, in shades of gray to bluish-gray. Reflectance percentages for the four COM wavelengths are [R-min, R-max (%), (lambda)]: 34.8, 36.4 (470 nm); 33.5, 35.1 (546 nm); 32.9, 35.0 (589 nm); and 31.8, 32.4 (650 nm). Electron-microprobe analysis gave (in wt% - average of seven spot analyses): Cu 1.06(2), Ag 11.25(18), Tl 0.45(9), Hg 2.76 (14), Pb 19.95(16), As 1.55(5), Sb 40.45(21), S 22.23(11), total 99.70(42). On the basis of Sigma Me= 40 atoms per formula unit, the chemical formula is Cu1.14Ag7.12Tl0.15Hg0.94Pb6.57(Sb22.68As1.41) S24.09S47.33, ideally CuAg7HgPb7Sb24S48. The main diffraction lines, corresponding to multiple hkl indices, are [d in angstrom (relative visual intensity)]: 3.719 (ms), 3.406 (s), 3.277 (s), 2.885 (s), 2.740 (ms), 2.131 (ms), 2.055 (s), and 1.788(s). The crystal structure study gave a monoclinic pseudo-orthorhombic unit cell, space group P2(1)/c, with a = 19.0982(14), b = 17.0093(11), c = 13.0008(10) angstrom, beta = 90.083(4)degrees, V = 4223.3(5) angstrom(3), Z = 2. The crystal structure was solved and refined to R-1 = 0.067 on the basis of 9756 reflections with F-o> 4 sigma(F-o) and 424 refined parameters. Andreadiniite is a new L-4,L-4 homologue belonging to the andorite sub-series of Sb-rich members within the lillianite homologous series. Antimony substituting Pb gives an ideal substitution percentage n = 106.25%. Distribution of minor cations (Hg, Cu, As) is detailed. Mercury may play a critical role for the stabilization of andreadiniite, through a complex substitution rule implying three cation sites: Pb2++Sb3++Ag+ -> Sb3++Ag++Hg2+. Copper is subordinate to the twoHg-rich sites. The name honors Andrea Dini (b. 1966) for his contribution to the knowledge of ore deposits from Tuscany and, in particular, the ore geology and mineralogy of Hg ores from Apuan Alps

Structural interpretation of a new twin in staurolite from Coray, Brittany, France

International audienceA new twin in staurolite has been recently reported from Coray (Brittany, France). From morphological measurements the twin plane has been identified as (202), which corresponds to twinning by reticular pseudomerohedry with index 3 and obliquity 0.97º. On the basis of the high-degree of lattice restoration, significantly higher than that in the other well-known twins in staurolite (Greek cross and Saint Andrews cross), one would expect a high probability of occurrence for this twin. Its rarity can be explained on structural bases. The interface corresponding to the twin plane corresponds to a highly disrupted coordination, where only half of the tetrahedra are restored. This makes a contact twin highly unlikely. The reported twin is actually a penetration twin, in which the irregular composition surface may have compensated, to some extent, the unfavourable structural match

Biagioniite, Tl 2 SbS 2 , from the Hemlo gold deposit, Marathon, Ontario, Canada: occurrence and crystal structure

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Another step toward the solution of the real structure of zinkenite

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Polygenic chamosite from a hydrothermalized oolitic ironstone (Saint-Aubin-des-Châteaux, Armorican Massif, France): crystal chemistry, visible-near-infrared spectroscopy (red variety) and geochemical significance

International audienceSeveral generations of chamosite, including a red variety, occur in the Ordovician hydrothermalized oolitic ironstone from Saint-Aubin-des-Châteaux (Armorican Massif, France). Their chemical re-examination indicates a low Mg content (0.925 < Fe/(Fe + Mg) < 0.954), but a significant variation in IV Al. Minor vanadium is present at up to 1.1 wt.% oxide. Variations in IV Al, the vanadium content and the colour of chamosite are related to the hydrothermal reworking of the ironstone. Taking into account other published data, the ideal composition of chamosite is (Fe 5-x Al 1+x)(Si 3-x Al 1+x)O 10 (OH) 8 , with 0.2 < x < 0.8 (0.2: equilibrium with quartz; 0.8: SiO 2 deficit). The red chamosite (IIb polytype) has a mean composition of (Fe 3.87 Mg 0.23 Mn 0.01 □ 0.07 Al 1.74 V 0.07)(Si 2.33 Al 1.67)O 10 (OH) 8. This chamosite is strongly pleochroic, from pale yellow (E || (001)) to deep orange red (E ⊥ (001)). Visible-near-infrared absorbance spectra show a specific absorption band centred at ∼550 nm for E ⊥ (001), due to a proposed new variety of Fe/V intervalence charge-transfer mechanism in the octahedral sheet, possibly Fe 2+-V 4+ → Fe 3+-V 3+. While the formation of green chamosite varieties is controlled by reducing conditions due to the presence of organic matter as a buffer, that of red chamosite would indicate locally a weak increase of f O 2 related to oxidizing hydrothermal solutions

Stoichiometric Arsenopyrite, FeAsS, from La Roche-Balue Quarry, Loire-Atlantique, France: Crystal Structure and Mossbauer Study

International audienceArsenopyrite from La Roche-Balue quarry (Loire-Atlantique department, France), with the stoichiometric composition FeAsS, has been studied by X-ray single-crystal diffraction and 57Fe Mössbauer spectroscopy. Its unit cell is a 5.7612(8), b 5.6841(7), c 5.7674(8) Å, β 111.721(8)°, and V 175.46(4) Å3 (Z = 4). Taking into account very fine ubiquitous twinning on {101}, its crystal structure has been refined in the space group P21/c on the basis of 758 unique reflections [Fo > 4σ(Fo)] to R1 = 0.0298. Within uncertainty limits, it indicates three unmixed Fe, As and S positions. The 57Fe Mössbauer spectrum of this arsenopyrite shows two broad absorption peaks that were fitted using the superposition of three doublets denoted as A, B and C, with parameters relative to area S, isomer shift δ, and quadrupole splitting ΔEQ, as follows: SA 82.2%, δA 0.24(1) mm/s, ΔEQA 1.12(2) mm/s; SB 8.5%, δB 0.25(1) mm/s, ΔEQB 0.69(2) mm/s; SC 9.3%, δC 0.26(1) mm/s, ΔEQC 1.49(2) mm/s. This set of values agrees well with the most recently published results for arsenopyrite samples with a composition close to stoichiometry. The three distinct Fe positions indicated by Mössbauer spectroscopy are not visible in the X-ray study. Whereas the main doublet A would seem to correspond to the FeAs3S3 octahedron of the ideal structure, the two minor doublets B and C, with a ΔEQ shift towards marcasite and löllingite, respectively, may be due to local disorder (e.g., twin contact walls) changing the octahedral coordination of Fe to unequal As:S ratios

The solid solutions of rebulite and jankovićite in the phase system Tl2S-As2S3-Sb2S3

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Lead-antimony sulfosalts from Tuscany (Italy). XXII. Marcobaldiite, ~Pb 12 (Sb 3 As 2 Bi) Σ6 S 21 , a new member of the jordanite homologous series from the Pollone mine, Valdicastello Carducci

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Suseinargiuite, (Na<SUB>0.5</SUB>Bi<SUB>0.5</SUB>)MoO<SUB>4</SUB>, the Na-Bi analogue of wulfenite, from Su Seinargiu, Sardinia, Italy

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