ALBERT

Description: The new mineral species boscardinite was discovered in the barite – pyrite – iron oxides deposit of Monte Arsiccio, near Sant’Anna di Stazzema, in the Apuan Alps, Tuscany, Italy. It forms a millimetric compact mass in a quartz vein embedded in dolomitic rocks. Other associated sulfides are stibnite and zinkenite. Boscardinite is metallic grey. Under the ore microscope, it is white; pleochroism is not discernible. Anisotropism is distinct, with an ubiquitous polysynthetic twinning; rotation tints are in shades of grey. Minimum and maximum reflectance data for COM wavelengths [λ (nm), Rair (%)] are: 470: 33.8/39.3, 546: 32.1/38.0, 589: 31.2/36.9, 650: 29.7/35.3. The hardness was not measured owing to the scarcity of the available material. Electron-microprobe analyses of two samples gave (wt. %, result mean of five analyses): 1) sample 4977: Ag 1.48(4), Tl 9.72(26), Pb 23.36(20), Sb 35.25(60), As 5.78(10), S 22.14(45), Se 0.04(1), total 97.77(90); 2) sample 4989: Ag 1.37(7), Tl 8.96(19), Pb 25.74(20), Sb 33.46(32), As 6.54(8), S 22.08(29), Se 0.01(1), total 98.16(63). On the basis of ∑Me = 14 apfu, they lead to the formulae Ag0.36Tl1.23Pb2.92(Sb7.50As2.00)∑9.50S17.88Se0.01 and Ag0.33Tl1.13Pb3.20(Sb7.09As2.25)∑9.34S17.76, respectively. A single-crystal X-ray study of boscardinite indicates triclinic symmetry, space group P1̄, with a 8.0929(4), b 8.7610(5), c 22.4971(11) Å, α 90.868(4), β 97.247(4), γ 90.793(4)°, V 1582.0(2) Å3, Z = 2. The d values (Å) of the main powder-diffraction lines, corresponding to multiple hkl indices, are (relative intensity visually estimated): 3.705 (ms), 3.540 (ms), 3.479 (m), 3.085 (m), 2.977 (ms), 2.824 (vs), 2.707 (s), 2.324 (ms), and 2.176 (ms). Boscardinite is the Tl–Sb homeotype of baumhauerite; its crystal structure has been solved by X-ray single-crystal study on the basis of 4319 observed reflections with a final R1 = 0.045. It can be described in the sartorite homologous series as formed by the 1:1 alternation of sartorite-type and dufrénoysite-type layers. The simplified structural formula is based on 18 sulfur atoms and can ideally be written as TlPb4(Sb7As2)∑9S18. The name boscardinite honors Matteo Boscardin for his contribution to knowledge of the regional mineralogy of Italy.

Description: Eldragónite, with the simplified formula Cu6BiSe4(Se2), is a new mineral species discovered in a telethermal vein-type deposit with selenides at the El Dragón mine, Province of Quijarro, Department of Potosí, Bolivia. It forms inclusions in krut’aite, and is associated with clausthalite, klockmannite, umangite and tiemannite, as well as with watkinsonite, petrovicite and two unnamed phases in the system Cu–Pb–Hg–Bi–Se. The unique vein of eldragónite-bearing krut’aite is hosted within sandstones and shales of Devonian age. Eldragónite occurs in anhedral grains and polycrystalline aggregates attaining a size of up to 100 × 80 μm. Megascopically, the mineral has a brownish to light-maroon color, is opaque and lacks internal reflections. It has a metallic luster and a brownish black streak, is brittle with an uneven to conchoidal fracture, without observable cleavage. The VHN15 values range between 212 and 243 (mean 225) kg/mm2, corresponding to a Mohs hardness of ~3 ½. In plane-polarized light, eldragónite is distinctly bireflectant and pleochroic, from light grayish brown to cream; it is strongly anisotropic with rotation tints in shades of orange and blue-black. The reflectances (in air and oil, respectively) for the COM standard wavelengths are: 32.5–34.5, 17.7–19.7 (470 nm), 32.95–36.3, 18.0–21.4 (546 nm), 33.3–36.8, 18.3–21.6 (589 nm), 34.0–36.9, 19.1–21.7 (650 nm). Electron-microprobe analyses gave (mean of 24 analyses): Cu 35.9, Fe 1.25, Ni 0.35, Bi 20.3, Se 42.5, total 100.3 wt.%, corresponding to (Cu5.98Fe0.24Ni0.06)∑6.28Bi1.03Se5.70. The ideal formula is Cu6BiSe4(Se2), which requires Cu 35.84, Bi 19.64, Se 44.52 wt.%. Eldragónite has an orthorhombic cell, space group Pmcn, with a 4.0341(4), b 27.056(3), c 9.5559(9) Å, V 1043.0(3) Å3, and Z = 4. The calculated density is 6.76 g/cm3. The strongest X-ray powder-diffraction lines [d in Å (I) hkl] are: 6.547(58)031, 3.579(100)052, 3.253(48)141, 3.180(77)081, 3.165(56)013, 3.075(84)102, 3.065(75)151,112, 2.011(53)200, 1.920(76)154, 1.846(52)1103. The crystal structure was solved from single-crystal data, and was refined to R1= 0.026 on the basis of 1731 unique reflections. There are one Bi and six Cu positions. Among the six Se positions, two Se atoms form a Se2 pair [d(Se–Se) = 2.413 Å]; eldragónite is thus a mixed selenide–diselenide compound. The crystal structure is organized according to two slabs alternating along a. The thin slab with formula Cu6Se6 is a zigzag layer derived from the CaF2 archetype; the thick slab, Cu6Bi2Se6, is similar to that of wittichenite, Cu3BiS3. The Se2 pair is at the junction between these two slabs. This new mineral species is named after the location where it was discovered.

Description: 〈div data-abstract-type="normal"〉 〈p〉Agmantinite, ideally Ag〈span〉2〈/span〉MnSnS〈span〉4〈/span〉, is a new mineral from the Uchucchacua polymetallic deposit, Oyon district, Catajambo, Lima Department, Peru. It occurs as orange–red crystals up to 100 μm across. Agmantinite is translucent with adamantine lustre and possesses a red streak. It is brittle. Neither fracture nor cleavage were observed. Based on the empirical formula the calculated density is 4.574 g/cm〈span〉3〈/span〉. On the basis of chemically similar compounds the Mohs hardness is estimated at between 2 to 2½. In plane-polarised light agmantinite is white with red internal reflections. It is weakly bireflectant with no observable pleochroism with red internal reflections. Between crossed polars, agmantinite is weakly anisotropic with reddish brown to greenish grey rotation tints. The reflectances (〈span〉R〈/span〉〈span〉min〈/span〉 and 〈span〉R〈/span〉〈span〉max〈/span〉) for the four standard wavelengths are: 19.7 and 22.0 (470 nm); 20.5 and 23.2 (546 nm); 21.7 and 2.49 (589 nm); and 20.6 and 23.6 (650 nm), respectively.〈/p〉 〈p〉Agmantinite is orthorhombic, space group 〈span〉P〈/span〉2〈span〉1〈/span〉〈span〉nm〈/span〉, with unit-cell parameters: 〈span〉a〈/span〉 = 6.632(2), 〈span〉b〈/span〉 = 6.922(2), 〈span〉c〈/span〉 = 8.156(2) Å, 〈span〉V〈/span〉 = 374.41(17) Å〈span〉3〈/span〉, 〈span〉a〈/span〉:〈span〉b〈/span〉:〈span〉c〈/span〉 0.958:1:1.178 and 〈span〉Z〈/span〉 = 2. The crystal structure was refined to 〈span〉R〈/span〉 = 0.0575 for 519 reflections with 〈span〉I 〉〈/span〉 2σ(〈span〉I〈/span〉). Agmantinite is the first known mineral of 〈span〉〈span〉〈img data-mimesubtype="gif" data-type="simple" src="http://static.cambridge.org/resource/id/urn:cambridge.org:id:binary:20190522072108342-0385:S0026461X18001391:S0026461X18001391_inline1.gif"〉 〈span data-mathjax-type="texmath"〉 〈/span〉 〈/span〉〈/span〉〈span〉M〈/span〉〈span〉II〈/span〉〈span〉M〈/span〉〈span〉IV〈/span〉S〈span〉4〈/span〉 type that is derived from wurtzite rather than sphalerite by ordered substitution of Zn, analogous to the substitution pattern for deriving stannite from sphalerite. The six strongest X-ray powder-diffraction lines derived from single-crystal X-ray diffraction data [〈span〉d〈/span〉 in Å (intensity)] are: 3.51 (s), 3.32 (w), 3.11 (vs), 2.42 (w), 2.04 (m) and 1.88 (m). The empirical formula (based on 8 apfu) is (Ag〈span〉1.94〈/span〉Cu〈span〉0.03〈/span〉)〈span〉Σ1.97〈/span〉(Mn〈span〉0.98〈/span〉Zn〈span〉0.05〈/span〉)〈span〉Σ1.03〈/span〉Sn〈span〉0.97〈/span〉S〈span〉4.03〈/span〉.The crystal structure-derived formula is Ag〈span〉2〈/span〉(Mn〈span〉0.69〈/span〉Zn〈span〉0.31〈/span〉)〈span〉Σ1.00〈/span〉SnS〈span〉4〈/span〉 and the simplified formula is Ag〈span〉2〈/span〉MnSnS〈span〉4〈/span〉.〈/p〉 〈p〉The name is for the composition and the new mineral and mineral name have been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA2014-083).〈/p〉 〈/div〉

Description: Georgerobinsonite, Pb4(CrO4)2(OH)2FCl, is a new chromate mineral species from the Mammoth - St. Anthony mine, Tiger, Pinal County, Arizona. It occurs as minute intergrowths of thin tabular orange crystals less than 0.1 mm across with {001} dominant and minor {010} and {110}, associated with caledonite, a cerchiaraite-related mineral, cerussite, diaboleite, Cr-bearing leadhillite, matlockite, murdochite, pinalite, wulfenite and yedlinite, in vugs in a silicified matrix. Georgerobinsonite is orange-red, transparent and has a pale orange streak and an adamantine luster, and it does not fluoresce under ultraviolet light. No cleavage or parting was observed. The Mohs hardness is 2[1/2]-3; georgerobinsonite is brittle with an uneven fracture. The calculated density is 6.23 g/cm3. The indices of refraction are {alpha} {approx} 2.07, {beta} 〉 2.11, {gamma} 〉 2.11; 2V(obs) = 84(2){degrees}; it is strongly pleochroic, {alpha} orange, {gamma} yellow; optical orientation: X = a, Y = c and Z = b, and the dispersion is strong with r 〉 v. Georgerobinsonite is orthorhombic, space group Pmmn, a 7.613(2), b 11.574(3), c 6.883(2) A, V 606.5(3) A3, Z = 2, a:b:c = 0.6578:1:0.5947. The strongest six lines in the X-ray powder-diffraction pattern [d in A(I)(hkl)] are: 2.131(100)(232), 3.308(80)(012), 3.195(80)(211, 220), 6.371(60) (110), 3.357(60)(031, 201) and 3.143(60)(102). Chemical analysis with an electron microprobe gave CrO3 14.79, PbO 77.99, SO3 1.64, F 1.47, Cl 3.39, H2O (calc.) 1.52, sum 99.42 wt.%; the valence states of Pb, Cr and S, and the amount of H2O, were determined by crystal-structure analysis. The resulting empirical formula, on the basis of 12 (O, F, Cl, OH) anions, is Pb4.09 (Cr6+1.73S6+0.24){sum}1.97 O8 (OH)1.98 F0.90 Cl1.12. The crystal structure of georgerobinsonite was solved by direct methods and refined to an R1 index of 2.0% based on 574 observed reflections collected on a four-circle diffractometer with MoK{alpha} X-radiation. There are two Pb2+ cations coordinated by eight and nine anions, and both show prominent lone-pair stereoactive behavior. The Pb polyhedra share faces and edges to form layers parallel to {001} that are linked into a heteropolyhedral framework by (CrO4) groups, with hydrogen bonding between OH and Cl anions. The mineral is named after Dr. George Willard Robinson (b. 1946), mineral curator, researcher, teacher and field collector.

Description: 〈div data-abstract-type="normal"〉〈p〉The crystal structure of the mineral gortdrumite, a rare copper-mercury-iron sulfide, was solved using intensity data collected using a crystal from the Neuschurf adit, Leogang, Salzburg, Austria. This study revealed that the structure is triclinic, space group 〈span〉P〈/span〉〈span〉〈span〉〈img data-mimesubtype="gif" data-type="simple" src="http://static.cambridge.org/resource/id/urn:cambridge.org:id:binary:20181017132303927-0397:S0026461X1800018X:S0026461X1800018X_inline1.gif"〉 〈span data-mathjax-type="texmath"〉 〈/span〉 〈/span〉〈/span〉, with cell parameters: 〈span〉a〈/span〉 = 9.677(4), 〈span〉b〈/span〉 = 9.865(5), 〈span〉c〈/span〉 = 11.992(5) Å, α = 77.85(4), β = 79.42(3), γ = 76.30(4)°, 〈span〉V〈/span〉 = 1076.5(8) Å〈span〉3〈/span〉 and 〈span〉Z〈/span〉 = 1. The refinement led to an 〈span〉R〈/span〉 index of 0.0833 for 3335 independent reflections and 143 parameters. Twelve S sites (one with half occupancy) and eighteen metal sites (5 Hg, 12 Cu and 1 Fe) occur in the crystal structure of gortdrumite. Mercury cations link two sulfur atoms in a linear coordination, Cu cations are found in various low-coordination (2, 3 and 4) sites, in agreement with the Cu preference for such environments, and Fe in tetrahedral coordination. Metal–metal interactions are also present and these contacts are discussed in relation with other copper sulfides, intermetallics and pure metals. Electron microprobe analyses of the crystal used for the structural study led to the formula Cu〈span〉24.83〈/span〉Fe〈span〉1.73〈/span〉Hg〈span〉9.09〈/span〉S〈span〉22.35〈/span〉, on the basis of 58 atoms. On the basis of information gained from the structural and chemical characterization, the crystal-chemical formula was revised to Cu〈span〉24〈/span〉Fe〈span〉2〈/span〉Hg〈span〉9〈/span〉S〈span〉23〈/span〉 (〈span〉Z〈/span〉 = 1) instead of (Cu,Fe)〈span〉6〈/span〉Hg〈span〉2〈/span〉S〈span〉5〈/span〉 as reported previously.〈/p〉〈/div〉