FGL Forschungsgemeinschaft Lengenbach

Milano, Italy

FGL Forschungsgemeinschaft Lengenbach

Milano, Italy

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Bindi L.,University of Florence | Bindi L.,CNR Institute of Geosciences and Earth Resources | Nestola F.,University of Padua | Graeser S.,University of Basel | And 2 more authors.
Mineralogical Magazine | Year: 2015

Eckerite, ideally Ag2CuAsS3, is a new mineral from the Lengenbach quarry in the Binn Valley, Valais, Switzerland. It occurs as very rare euhedral crystals up to 300 μm across associated with realgar, sinnerite, hatchite, trechmannite and yellow, fibrous smithite. In thick section eckerite is opaque with a metallic lustre and shows a dark orange-red streak. It is brittle; the Vickers hardness (VHN25) is 70 kg/mm2 (range: 64-78) (Mohs hardness of ∼2-3). In reflected light, eckerite is moderately bireflectant and weakly pleochroic from light grey to a slightly bluish grey. Internal reflections are absent. Under crossed nicols, it is weakly anisotropic with greyish to light blue rotation tints. Reflectance percentages for R min and R max are 27.6, 31.7 (471.1 nm), 22.8, 26.1 (548.3 nm), 21.5, 24.5 (586.6 nm) and 19.4, 22.3 (652.3 nm), respectively. Eckerite is monoclinic, space group C2/c, with a = 11.8643(3), b = 6.2338(1), c = 16.6785(4) Å, β = 110.842(3)°, V = 1152.81(5) Å3, Z = 8. The crystal structure [R 1 = 0.0769 for 1606 reflections with F o > 4σ(F o)] is topologically identical to that of xanthoconite and pyrostilpnite. In the structure, AsS3 pyramids are joined by AgS3 triangles to form double sheets parallel to (001); the sheets are linked by Cu(Ag) atoms in a quasi-tetrahedral coordination. Among the three metals sites, Ag2 is dominated by Cu. The mean metal-S distances reflect well the Ag â†" Cu substitution occurring at this site. The eight strongest powder X-ray diffraction lines [d in Å (I/I0 ) (hkl)] are: 3.336 (70) (312); 2.941 (100) (314,114); 2.776 (80) (400,206); 2.677 (40) (312); 2.134 (50) (421); 2.084 (40) (208,206); 2.076 (40) (420); 1.738 (40) (228,226). A mean of five electron microprobe analyses gave Ag 52.08(16), Cu 11.18(9), Pb 0.04(1), Sb 0.29(3), As 15.28(11), S 20.73(13), total 99.60 wt.%, corresponding, on the basis of a total of 7 atoms per formula unit, to Ag2.24Cu0.82As0.94Sb0.01S2.99. The new mineral has been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (2014-063) and named for Markus Ecker, a well known mineral expert on the Lengenbach minerals for more than 25 years. © 2015 Mineralogical Society.


Bindi L.,University of Florence | Bindi L.,CNR Institute of Geosciences and Earth Resources | Nestola F.,University of Padua | Makovicky E.,Copenhagen University | And 2 more authors.
Mineralogical Magazine | Year: 2014

Philrothite, ideally TlAs3S5, is a new mineral from the Lengenbach quarry in the Binn Valley, Valais, Switzerland. It occurs as very rare crystals up to 200 mm across on realgar associated with smithite, rutile and sartorite. Philrothite is opaque with a metallic lustre and shows a dark brown streak. It is brittle; the Vickers hardness (VHN25) is 128 kg/mm2 (range: 120137) (Mohs hardness of 33). In reflected light philrothite is moderately bireflectant and weakly pleochroic from dark grey to light grey. Under crossed polars it is anisotropic with grey to bluish rotation tints. Internal reflections are absent. Reflectance percentages for the four COM wavelengths (Rmin and Rmax) are: 26.5, 28.8 (471.1 nm), 25.4, 27.2 (548.3 nm), 24.6, 26.3 (586.6 nm) and 24.0, 25.1 (652.3 nm), respectively. Philrothite is monoclinic, space group P21/c, with a = 8.013(2), b = 24.829(4), c = 11.762(3) Å , b = 132.84(2)°, V = 1715.9(7) Å 3, Z = 8. It represents the N = 4 homologue of the sartorite homologous series. In the crystal structure [R1 = 0.098 for 1217 reflections with I > 2s(I)], Tl assumes tricapped prismatic sites alternating to form columns perpendicular to the b axis. Between the zigzag walls of Tl coordination prisms, coordination pyramids of As(Sb) form diagonally-oriented double layers separated by broader interspaces which house the lone electron pairs of these elements. The eight strongest calculated powder-diffraction lines [d in Å (I/I0) (hkl)] are: 12.4145 (52) (020); 3.6768 (100) (1- 61); 3.4535 (45) (131); 3.0150 (46) (1-53); 2.8941 (52) (1-81); 2.7685 (76) (230); 2.7642 (77) (2-34); 2.3239 (52) (092). A mean of five electron microprobe analyses gave Tl 26.28(12), Pb 6.69(8), Ag 2.50(4), Cu 0.04(2), Hg 0.07(2), As 32.50(13), Sb 3.15(3), S 26.35(10), total 97.58 wt.%, corresponding, on the basis of a total of nine atoms, to (Tl0.789Pb0.198)S=0.987 (As2.662Sb0.159Ag0.142Cu0.004Hg0.002) S=2.969S5.044. The new mineral has been approved by the Commission on New Minerals, Nomenclature and Classification (CNMNC) of the International Mineralogical Association (2013-066) and named for Philippe Roth (b. 1963), geophysicist and well known mineral expert on the Lengenbach minerals for more than 25 years. © 2014 The Mineralogical Society.


Biagioni C.,University of Pisa | Bindi L.,University of Florence | Nestola F.,University of Padua | Cannon R.,FGL Forschungsgemeinschaft Lengenbach | And 2 more authors.
Mineralogical Magazine | Year: 2016

The new mineral species ferrostalderite, CuFe2TlAs2S6, was discovered in the Lengenbach quarry, Binn Valley, Wallis, Switzerland. It occurs as minute, metallic, black, equant to prismatic crystals, up to 50 μm, associated with dolomite, realgar, baumhauerite (?) and pyrite. Minimum and maximum reflectance data for COM wavelengths in air are [λ (nm): R (%)]: 471.1: 24.2/25.4; 548.3: 23.7/24.7; 586.6: 22.9/23.8; 652.3: 21.0/22.0. Electron microprobe analyses give (wt.%): Cu 6.24(25), Ag 4.18(9), Fe 9.95(83), Zn 4.46(91), Hg 1.22(26), Tl 26.86(62), As 19.05(18), Sb 0.63(6), S 25.39(47), total 97.98(72). On the basis of 12 atoms per formula unit, the chemical formula of ferrostalderite is Cu0.75(2)Ag0.30(1)Fe1.36(10)Zn0.52(11)Hg0.05(1)Tl1.00(1)[As1.94(4)Sb0.04(1)]λ1.98(4)S6.04(4). The new mineral is tetragonal, space group I42 m,with a = 9.8786(5), c = 10.8489(8) Å, V = 1058.71(11) Å3, Z = 4. The main diffraction lines of the calculated powder diagram are [d (in Å), intensity, hkl]: 4.092, 70, 211; 3.493, 23, 220; 3.396, 35, 103; 3.124, 17, 310; 2.937, 100, 222; 2.656, 19, 321; 2.470, 19, 400; 2.435, 33, 303. The crystal structure of ferrostalderite has been refined by X-ray single-crystal data to a final R1 = 0.050, on the basis of 1169 reflections with F0 > 4σ(F0). It shows a three dimensional framework of (Cu,Fe)-centred tetrahedra (1M1 + 2M2), with channels parallel to [001] hosting disymmetric TlS6 and (As,Sb)S3 polyhedra. Ferrostalderite is derived from its isotype stalderite M1CuM2Zn2TlAs2S6 through the homovalent substitution M2Zn2+ → M2Fe2+. The ideal crystal-chemical formula of ferrostalderite is M1CuM2Fe2TlAs2S6. © 2016 by Walter de Gruyter Berlin/Boston 2016.


Bindi L.,University of Florence | Biagioni C.,University of Pisa | Raber T.,FGL Forschungsgemeinschaft Lengenbach | Roth P.,FGL Forschungsgemeinschaft Lengenbach | Nestola F.,University of Padua
Mineralogical Magazine | Year: 2015

The new mineral species ralphcannonite, AgZn2TlAs2S6, was discovered in the Lengenbach quarry, Binn Valley, Wallis, Switzerland. It occurs as metallic black equant, isometric to prismatic crystals, up to 50 μm, associated with dufrenoysite, hatchite, realgar and baryte. Minimum and maximum reflectance data for COM wavelengths in air are [λ (nm): R (%)]: 471.1: 25.8/27.1; 548.3: 25.2/26.6; 586.6: 24.6/25.8; 652.3: 23.9/24.8. Electron microprobe analyses give (wt.%): Cu 2.01(6), Ag 8.50( 16), Zn 10.94(20), Fe 3.25(8), Hg 7.92(12), Tl 24.58(26), As 18.36(19), Sb 0.17(4), S 24.03(21), total 99.76(71). On the basis of 12 atoms per formula unit, the chemical formula of ralphcannonite is Ag0.63(2)Cu0.25(2)Zn1.35(5)Fe0.47(1)Hg0.32(2)Tl0.97(3)[As1.97(6)Sb0.01(1)]Σ1.9(8)S6.03(8). The new mineral is tetragonal, space group I4 2m, with a =9.861 (2), c= 11.125(3) Å, V= 1081.8(4) Å3, Z= 4. The main diffraction lines of the calculated powder diagram are [d(in Å), intensity, hkl]: 4.100, 85, 211; 3.471,40, 103; 2.954, 100, 222; 2.465, 24, 400; 2.460,39, 303. The crystal structure of ralphcannonite has been refined by X-ray single-crystal data to a final Ri =0.030, on the basis of 140 observed reflections [F0> 4σ(F0)]. It shows a three dimensional framework of (Ag,Zn)- centred tetrahedra (1 M1 + 2 M2), with channels parallel to [001] hosting TlS6 and (As5Sb)S3 disymmetric polyhedra. Ralphcannonite is derived from its isotype routhierite M1iCuM2Hg2TlAs2S6 through the double heterovalent substitution M1Cu+ + M2Hg2+→ M1Zn2+ + M2Ag+. This substitution obeys a steric constraint, with Ag+, the largest cation relative to Zn2+ and Cu+, entering the largest Ml site, as observed in arsiccioite. The ideal crystal-chemical formula of ralphcannonite is M1ZmM2(Zn0.5Ag0.5)2TlAs2S6. © 2015 by Walter de Gruyter Berlin/Boston.


Bindi L.,University of Florence | Bindi L.,CNR Institute of Geosciences and Earth Resources | Makovicky E.,Copenhagen University | Nestola F.,University of Padua | De Battisti L.,FGL Forschungsgemeinschaft Lengenbach
Canadian Mineralogist | Year: 2013

We have characterized the crystal structure of sinnerite, Cu6As4S9, a rare sulfosalt mineral from the ores of the Lengenbach quarry, Binn Valley, Canton Valais, Switzerland, by single-crystal X-ray diffraction and chemical analysis. We found sinnerite to be structurally identical to synthetic Cu6As4S9. It is triclinic, space group P1, with cell parameters: a 9.103(2), b 9.860(3), c 9.111(2) Å, α 90.27(2), β 109.53(2), γ 107.58(2)° , V 729.6(4) Å3, and Z = 2. Semi-quantitative SEM-EDS analyses confirmed the Cu6As4S9 stoichiometry. The crystal structure of an untwinned crystal has been refined to R1 = 5.45%. It consists of a sphalerite substructure with 2/5 of the tetrahedra replaced by AsS3 pyramids; four pyramids form As4S12 clusters around the vacant anion positions of the sphalerite archetype. These pyramids are linked into twisted and branched chain-like structures with compositions As3S7 and As5S11. The chains are linked by CuS4 tetrahedra. Packing of these chains results in the OD (order-disorder) character of the sinnerite structure.


Bindi L.,University of Florence | Nestola F.,University of Padua | De Battisti L.,FGL Forschungsgemeinschaft Lengenbach | Guastoni A.,University of Padua
Mineralogical Magazine | Year: 2013

Dervillite, As2AsS2, has been found in a sample from the Lengenbach quarry in the Binn Valley, Valais, Switzerland. It occurs as very rare crystals up to 200 μm across on jordanite. Dervillite is opaque with a metallic lustre and shows a dark brown streak. The structure is monoclinic, space group Pc, with a = 9.6155(7), b = 12.9331(8), c = 6.8616(5) A Ëš , b = 99.352(8)°, V = 842.0(1) Å3 and Z = 8. In the crystal structure [R 1 = 0.060 for 2370 reflections with I > 2σ(I)], silver adopts various coordinations extending from quasi linear to quasi tetrahedral whereas arsenic forms very peculiar crystal-chemical environments, such as As(S2As) and As(S2AsAg). Such metalloid-metalloid or metal-metalloid bonds account for the apparent charge imbalance observed in the chemical formula. © 2013 Mineralogical Society.

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