ALBERT

Description: A bstract Three specimens of galkhaite from the Getchell mine (G), Nevada, USA; the Gal-Khaya As-Hg-Sb deposit (Gk), Yakutia, Russia; and Signols (S), Piedmont, Italy, have been fully characterized through single-crystal X-ray diffraction and electron-microprobe analyses. Chemical data indicate the formulae [(Hg 4.61 Zn 0.38 Fe 0.04 ) 5.03 (Cu 1.03 Ag 0.04 ) 1.07 ] 6.10 (Cs 0.76 Tl 0.20 ) 0.96 (As 3.81 Sb 0.04 ) 3.85 S 12.06 (G), [(Hg 4.66 Zn 0.32 ) 4.98 (Cu 0.55 Ag 0.45 ) 1.00 ] 5.98 (Cs 0.74 Tl 0.06 ) 0.80 (As 3.42 Sb 0.56 ) 3.98 S 12.05 (Gk), and [(Hg 4.10 Zn 0.85 ) 4.95 (Cu 0.89 Ag 0.16 ) 1.05 ] 6.00 Cs 0.95 (As 3.64 Sb 0.16 ) 3.80 S 12.19 (S). Unit-cell parameters are a 10.405(3) Å (G), 10.443(1) Å (Gk), and 10.332(2) Å (S), space group I 4 {macron} 3 m . The crystal structure of the three specimens has been solved to R 1 = 0.029 (G), 0.028 (Gk), and 0.031 (S). It is a three-dimensional framework of HgS 4 and AsS 3 polyhedra, with Cs hosted in large 12-fold coordinated cavities. The introduction of Cs + , as well as minor Tl + , at these structural positions requires the replacement of Hg 2+ by Cu + . The mixed site occupancy at the Hg site of galkhaite is a case of valency-imposed double site-occupancy. Consequently, the idealized chemical formula of galkhaite can be written as (Hg 5 Cu)CsAs 4 S 12 . Taking into account the possible existence of vacancy in the structural cavities, the formula can be generalized as (Hg 5+ x Cu 1– x ) 6 Cs 1– x As 4 S 12 ( x 0).

Description: Bonazziite is a new mineral from Khaidarkan deposit, Kyrgyzstan and represents the natural analogue of the β-form of the well known As 4 S 4 compound. It occurs as rare crystals up to 100 μm across associated with realgar, sulfur, wakabayashilite, alacránite, non-stoichiometric As 4 S 4+ x sulfides and stibnite in a calcite matrix. In thick section, bonazziite is opaque with a resinous lustre and a dark-orange streak. It is brittle; the Vickers hardness (VHN 15 ) is 70 kg/mm 2 (range: 60–76) (Mohs hardness of ~21/2). In plane-polarized incident light, bonazziite is strongly bireflectant and pleochroic from orange to light red. The mineral shows orange to red internal reflections. Between crossed polars, the mineral is strongly anisotropic with greyish to light-blue rotation tints. Reflectance percentages in air for R min and R max are 19.9, 22.2 (471.1 nm), 19.1, 21.3 (548.3 nm), 18.8, 19.7 (586.6 nm) and 17.8, 18.9 (652.3 nm), respectively. Bonazziite is monoclinic, space group C 2/ c , with a = 9.956(1), b = 9.308(1), c = 8.869(1) Å, β = 102.55(2)° and V = 802.3(2) Å 3 , Z = 4. The crystal structure [ R 1 = 0.0263 for 735 reflections with F o 〉 4( F o )] is based on the As 4 S 4 cage-like molecule, in which each As atom links one As and two S atoms. The As 4 S 4 molecule is identical to that found in the structure of realgar. The six strongest powder diffraction lines [ d in Å ( I/I 0 ) ( hkl )] are: 5.74 (100) (1I11); 4.10 (60) (021); 3.92 (50) (1I12); 3.12 (60) (022, 310); 2.95 (50) (221, 202); 2.86 (80) (2I22, 1I31). A mean of six electron microprobe analyses gave the formula As 3.95 S 4.05 , on the basis of eight atoms. The new mineral has been approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA No. 2013-141) and named for Paola Bonazzi, in recognition of her seminal contributions to the study of arsenic sulfides and their alteration induced by exposure to light.

Description: The crystal structure of the spinel-related, Sb mineral tegengrenite from the Filipstad district, Värmland, Sweden, has been solved in the space group R 3 [ a = 16.0285(9), c = 14.8144(8) Å, V = 3296.1(3) Å 3 , Z = 42] and refined up to R = 0.0484 for 3589 reflections with F o 〉 4( F o ). Tegengrenite exhibits a rhombohedrally distorted spinel-type structure with cations occupying 1/8 of the tetrahedral (T) and 1/2 of the octahedral (M) interstices of a nearly regular cubic close-packing of oxygen atoms. Due to the cation ordering, which leads to a complex superstructure with a unit-cell volume of 21/4 that of a common spinel, the M and T sites of the spinel-type structure split into ten and six independent sites, respectively. Chemical composition determined by electron microprobe led to the empirical formula Mg 1.26 $${\mathrm{Mn}}_{0.85}^{2+}$$ Zn 0.04 $${\mathrm{Mn}}_{0.19}^{3+}$$ Al 0.01 Si 0.12 Ti 0.03 $${\mathrm{Sb}}_{0.50}^{5+}$$ O 4 , on the assumption that no vacancies occur in the mineral ( cat = 3.00 and charge = 8.00 per formula unit). Crystal-chemical considerations indicate that octahedra are occupied mainly by Mg, Mn 3+ and Sb 5+ (+Al, + Ti), whereas tetrahedra are filled mainly by Mn 2+ and Mg (+Zn) with Si ordered in a specific site. However, the structure refinement shows a low site-scattering factor for one octahedral site, implying substantial vacancies and a larger overall mean Mn valence than stated above. Long mean distances also suggest some Mn 2+ on octahedral sites. Together, these observations necessitate the presence of substantial Mn 3+ on tetrahedral sites.

Description: We designed a plate impact shock recovery experiment to simulate the starting materials and shock conditions associated with the only known natural quasicrystals, in the Khatyrka meteorite. At the boundaries among CuAl5, (Mg0.75Fe2+0.25)2SiO4 olivine, and the stainless steel chamber walls, the recovered specimen contains numerous micron-scale grains of a quasicrystalline...

Description: A mica-group mineral characterized by a high V content and free of Al was found in the manganesiferous beds within the metacherts of the ophiolitic sequences at the Cerchiara mine, Eastern Liguria (Italy), in association with hematite, quartz, and calcite. Chemical and structural characterization supported by Raman data defines this phase as a new mineral species, which is named balestraite after Corrado Balestra, a prominent Italian amateur mineralogist. Balestraite, ideally KLi 2 V 5+ Si 4 O 10 O 2 , is a 1 M trioctahedral mica crystallizing in the C 2 space group, with a = 5.2024(5), b = 8.9782(7), c = 9.997(2) Å, β = 100.40(2)°, V = 459.3(1) Å 3 , Z = 2. The reduction of symmetry from the "ideal" space group C 2/ m is related to the ordering of V at only one of the two pseudo-symmetric octahedral sites. Vanadium forms very distorted octahedra with a [2+2+2] geometry characteristic of the valence state +5. The Li,V composition of the octahedral sheet, the pure tetrasilicic character of the tetrahedral sheet, and the anhydrous character produce unusual geometrical features for this mica. The occurrence of 5+ as the dominant valence state of V and the virtually complete O 2– -〉 OH – substitution at the O4 site indicate strongly oxidizing conditions of crystallization, which are consistent with balestraite occurring at the boundary between carbonate-bearing veins and hematite bands. The new mineral and name were approved by the Commission on New Minerals, Nomenclature and Classification, IMA (2013-080).

Description: The crystal structure of the rare mineral dalnegroite, Tl5-xPb2x(As,Sb)21-xS34 with x {approx} 1, was determined for a crystal from Lengenbach, Binn Valley, Switzerland. The structure is triclinic, space group P1, with a = 16.218(3), b = 42.546(7), c = 8.558(1) A, {alpha} = 95.70(4), {beta} = 90.18(3), {gamma} = 96.38(4){degrees}, V = 5838.9(9) A3, Z = 4. Refinement of an isotropic model led to an R1 index of 0.0536 for 22226 observed reflections and 980 parameters, and R1 = 0.0590 for all 25266 independent reflections. Although dalnegroite cannot be considered a layered compound, its structure can be usefully described as a regular alternation of two kinds of layers stacked along the b axis, with four layers in the unit cell: (1) a layer 7.8 A thick, at y {approx} 0.15 and 0.65, can be considered as derived from the SnS archetype; (2) a layer 13.6 A thick, at y {approx} 0.35 and 0.85, derived from the PbS archetype. Different chemical compositions, such as Tl:Pb and Sb:As ratios, for different samples belonging to the chabourneite-dalnegroite family could play a central role in controlling different degrees of order, leading to different superstructures.

Description: Fassinaite, ideally Pb2+2(S2O3)(CO3), is a new mineral from the Trentini mine, Mount Naro, Vicenza Province, Veneto, Italy (holotype locality). It is also reported from the Erasmus adit, Schwarzleo District, Leogang, Salzburg, Austria and the Friedrich-Christian mine, Schapbach, Black Forest, Baden-Württemberg, Germany (cotype localities). At the Italian type locality it occurs as acicular [010], colourless crystals up to 200 µm long, closely associated with galena, quartz and anglesite. At the Austrian cotype locality it is associated with cerussite, rare sulphur and very rare phosgenite. At the German cotype locality anglesite is the only associated phase. Fassinaite crystals commonly have flat chisel-shaped terminations. They are transparent with vitreous to adamantine lustre and a white streak. Fassinaite is brittle with an irregular fracture and no discernible cleavage; the estimated Mohs hardness is 1½–2. The calculated density for the type material is 6.084 g cm-3 (on the basis of the empirical formula), whereas the X-ray density is 5.947 g cm-3. In common with other natural lead thiosulphates (i.e. sidpietersite and steverustite) fassinaite has intense internal reflections, which do not allow satisfactory optical data to be collected; the crystals are length-slow and have very high birefringence. The mineral is not fluorescent.Fassinaite is orthorhombic, space group Pnma, with unit-cell parameters (for the holotype material) a = 16.320(2), b = 8.7616(6), c = 4.5809(7) Å, V = 655.0(1) Å3, a:b:c = 1.863:1:0.523, Z = 4. Single-crystal structural studies were carried out on crystals from all three localities: R1(F) values range between 0.0353 and 0.0596. The structure consists of rod-like arrangements of Pb-centred polyhedra that extend along the [010] direction. These ‘rods’ are linked, alternately, by (CO3)2- and (S2O3)2- groups. The (S2O3)2- groups point alternately left and right (in a projection on [001] with [010] set vertical) if the apex occupied by the S2- in the thiosulphate group is defined to be the atom giving the direction. The lead atoms are nine-coordinated by seven oxygen atoms and two sulphur (S2-) atoms. The eight strongest X-ray powder-diffraction lines [d in Å (I/I0) (hkl)] are: 4.410 (39) (101), 4.381 (59) (020), 4.080 (62) (400), 3.504 (75) (301), 3.108 (100) (121), 2.986 (82) (420), 2.952 (49) (221) and 2.736 (60) (321). Electron-microprobe analyses produce an empirical formula Pb2.01(1)(S1.82(2)O3)CO3 (on the basis of six oxygen atoms). The presence of both carbonate and thiosulphate groups was corroborated by Raman spectra, which are discussed in detail. Fassinaite is named after Bruno Fassina (b. 1943), an Italian mineral collector who discovered the mineral in 2009.