Désorite, Pb₂(Fe³⁺₆Zn)O₂(PO₄)₄(OH)₈, a New Phosphate Mineral Isotypic with Jamesite

The new mineral désorite, Pb2(Fe3+6Zn)O2(PO4)4(OH)8, is a secondary oxidation-zone mineral discovered on the dumps of the Schöne Aussicht mine, Dernbach, Westerwaldkreis, Rhineland-Palatinate, Germany. The crystals are irregular blades up to about 0.25 mm long, occurring in subparallel and radial aggregates. Désorite is brownish red. It has an orange streak, adamantine luster, brittle tenacity, splintery and curved fracture and two cleavages: {021¯} perfect and {001} good. It has a hardness (Mohs) of about 3 and is nonfluorescent in both long- and short-wave ultraviolet illumination. The calculated density is 4.633 g/cm3. Optically, crystals are biaxial (+) with α = 2.00(1), β = 2.02(calc) and γ = 2.10(calc) (white light). The 2V is 54(2)° and the optical orientation is Y ~⊥{021¯}, X ∧ a ≈ 13°. The mineral is pleochroic: X yellow brown, Y red brown, Z red brown; X Y ≈ Z. The empirical formula from electron microprobe analysis is Pb1.93(Zn0.50Fe3+6.29☐0.21)Σ7.00(P3.90As0.10)Σ4.00O26H8.28. Désorite is triclinic, space group P1¯; the unit-cell parameters are a = 5.4389(7), b = 9.3242(13), c = 10.0927(12) Å, α = 109.024(8), β = 90.521(6), γ = 97.588(7)°, V = 478.90(11) Å3 and Z = 1. Désorite has a framework structure (R1 = 0.0487 for 937 I > 2σI reflections) assembled from Fe3+O6 octahedra and PO4 tetrahedra, with Pb occupying cavities in the framework. The Fe3+O6 octahedra in the framework occur in edge-sharing chains, edge-sharing trimers and individual octahedra, all sharing corners with each other and with PO4 tetrahedra. Désorite is isostructural with jamesite and lulzacite

Cuatrocapaite-(NH4) and cuatrocapaite-(K), two new minerals from the Torrecillas mine, Iquique Province, Chile, related to lucabindiite and gajardoite

The new minerals cuatrocapaite-(NH4) (IMA2018-083) and cuatrocapaite-(K) (IMA2018-084) are the NH4- and K-dominant members of a series with the general formula (NH4,K)3(NaMg□)(As2O3)6Cl6·16H2O. Both minerals were found at the Torrecillas mine, Iquique Province, Chile, where they occur as secondary alteration phases. Both minerals occur as hexagonal tablets up to ~0.3 mm in diameter. They are transparent, with a vitreous lustre and white streak. For both, the Mohs hardness is ca. 2½, the crystals are somewhat flexible, but not elastic, the fracture is irregular and the cleavage is perfect on {001}. The measured densities are 2.65(2) and 2.76(2) g/cm3 for the NH4- and K-dominant species, respectively. Optically, cuatrocapaite-(NH4) is uniaxial (–) with ω = 1.779(3) and ε = 1.541(3) and cuatrocapaite-(K) is uniaxial (–) with ω = 1.777(3) and ε = 1.539(3) (white light). The minerals are insoluble in acids, but decompose in NaOH(aq). The empirical formulas, determined from electron-microprobe analyses, are (NH4)2.48Na1.66Mg0.87K0.09(As12O18.05)Cl5.88·16.02H2O and K2.68Na1.33Mg0.93(NH4)0.31(As12O18.01)Cl6.16·16.04H2O. The minerals are trigonal, space group R m; the cuatrocapaite-(NH4) cell parameters are a = 5.25321(19), c = 46.6882(19) Å, V = 1115.80(9) Å3 and Z = 1; the cuatrocapaite-(K) cell parameters are a = 5.2637(15), c = 46.228(8) Å, V = 1109.2(7) Å3 and Z = 1. The structures, refined for cuatrocapaite-(NH4) to R1 = 1.78% for 544 Io > 2σI reflections, contain four types of layers: (1) a planar neutral As2O3 (arsenite) sheet; (2) an ( ,K+) layer that links adjacent arsenite sheets; (3) a Cl– layer placed on the As side of each arsenite; and (4) a layer containing partially occupied Na, Mg and H2O sites that is flanked on either side by Cl layers. The layer sequence for the type 1, 2 and 3 layers is identical to the Cl–As2O3–K–As2O3–Cl layer sequence in the structures of lucabindiite and gajardoite

A New Mineral Hanauerite, AgHgSI, and Common Crystal Chemical Features of Natural Mercury Sulphohalides

A new mineral, hanauerite, ideally AgHgSI, was found in the oxidation zone of Ag- and Hg-bearing ores at two old, abandoned mines in Rhineland-Palatinate, Germany. In a holotype specimen originating from the Schöne Aussicht Mine, Dernbach, Westerwald, it is associated with plumbogummite–hinsdalite series of minerals and goethite. In cotype from the Friedrichssegen Mine, Bad Ems, it is associated with perroudite, goethite, and quartz. At both localities, hanauerite occurs as a prismatic crystal up to 0.15 mm long and up to 0.02 mm thick. The mineral is yellow, transparent, with an adamantine lustre. It is brittle, and cleavage was not observed. The calculated density values are 6.671 and 6.575 g cm−3 for holotype and cotype, respectively. The empirical formulae calculated (from electron microprobe data) based on the sum of all atoms = 4 apfu are Ag0.95Hg1.00S1.01(I0.83Br0.19Cl0.03)Σ1.05 for holotype and Ag0.97Hg0.97S1.05(I0.76Br0.25)Σ1.01 for cotype. Hanauerite is orthorhombic, space group Pmma; the unit cell parameters (from single-crystal X-ray diffraction data; holotype/cotype) are: a = 9.932(2)/9.9256(8), b = 4.6219(19)/4.6209(2), c = 9.891(4)/9.9006(4) Å, V = 454.0(3)/454.19(5) Å3, and Z = 4. The crystal structure was studied on single crystals extracted from both holotype and cotype specimens; R1 = 0.0416 (holotype) and =0.0544 (cotype). In hanauerite, Hg2+ cations centre strongly distorted octahedra with two short Hg–S bonds (Hg and S atoms build “crankshaft-type” chains) and four strongly elongated Hg–I bonds. The Hg-centred octahedra are connected via common edges and faces to form corrugated layers; Ag+ cations are located between these layers. Hanauerite is named in honour of the German mineral collector Dr. Alfred Hanauer (1912–1988). The common crystal chemical features of mercury sulphohalide minerals are discussed