Arsenáty mědi z dobývky na žíle Geschieber - sever (patro Daniel), Svornost, jáchymovský rudní revír (Česká republika)
Authors: Sejkora Jiří , Bureš Bohuslav 
Published: December 2020

An interesting mineral association of Cu arsenates was found at abandoned ore stope at the Geschieber vein - north at the Daniel level of the Svornost mine, the Jáchymov ore district, Krušné hory, Czech Republic. Tangdanite forms thin tabular crystals up to 3 mm in size and coatings and fine crystalline aggregates on the area up to some cm2. It has light green, bluish-green to emerald green color and perfect cleavage. It is monoclinic, space group C2/c, the unit-cell parameters refined from X-ray powder diffraction data are: a 54.335(12), b 5.579(2), c 10.459(2) Å, β 95.42(3)° and V 3156(2) Å3; its chemical analyses correspond to the empirical formula Ca1.99(Cu8.72Zn0.09Ni0.04Al0.04)Σ8.89[(AsO4)3.83 (PO4)0.14(SiO4)0.03]Σ4.00(SO4)0.41(OH)8.97·9H2O on the basis As+P+Si+V = 4 apfu. The results of Raman and infrared spectroscopy confirmed an absence of carbonate group in studied tangdanite. K-rich lavendulan was found as a relatively abundant sky blue crusts and coatings on the area up to some cm2 and hemispherical aggregates with a radial structure or rarely as a group of thin tabular crystals up to 0.2 mm in size. It is monoclinic, space group P21/n, the unit-cell parameters refined from X-ray powder diffraction data are: a 10.081(12), b 19.469(12), c 10.033(9) Å, β 90.32° and V 1969(2) Å3; its chemical analyses correspond to the empirical formula (Na0.63K0.16)Σ0.79Ca1.12(Cu4.82Al0.01)Σ4.83[(AsO4)3.86(PO4)0.07 (SO4)0.06(SiO4)0.01]Σ4.00Cl0.96·5H2O on the basis As+P+V+Si+S = 4 apfu. Olivenite occurs as olive green spherical aggregates with radial structure up to 8 mm in size and rarely as groups of acicular crystals in association with strashimirite and köttigite. It is orthorhombic, space group Pnnm, the unit-cell parameters refined from X-ray powder diffraction data are: a 8.6204(10), b 8.2332(9), c 5.9337(11) Å and V 421.13(7) Å3; its chemical analyses correspond to the empirical formula (Cu1.94Ni0.01Al0.01)Σ1.96[(AsO4)0.97(VO4)0.02(PO4)0.01]Σ1.00(OH)0.93 on the basis As+V+P = 1 apfu. Strashimirite forms there light green crystalline coatings on the area up to several cm2 and spherical aggregates with a radial structure in association with olivenite and lavendulan. Strashimirite is probably monoclinic, space group P2, the unit-cell parameters refined from X-ray powder diffraction data are: a 9.991(9), b 18.466(9), c 8.986(8) Å, β 96.5(2)° and V 1574(3) Å3; its chemical analyses correspond to the empirical formula (Cu7.83Ni0.18Ca0.09Zn0.06Co0.02Al0.02)Σ8.20 [(AsO4)3.81(PO4)0.07 (SO4)0.07(VO4)0.03(SiO4)0.02]Σ4.00 (OH)4.45·5H2O on the basis As+P+Si+V+S = 4 apfu. Chalcophyllite was found as rare emerald green thin tabular crystals up to 0.5 mm in size and crystalline aggregates. Its chemical composition is possible to express on the basis As+S+P+Si = 7 apfu by the empirical formula Cu17.83Al1.97[(AsO4)4.00(PO4)0.09]Σ4.09[(SO4)2.80(SiO4)0.11]Σ2.91
(OH)23.27·36H2O. Brochantite, devilline, köttigite, erythrite and gypsum were also found in the association with Cu arsenates. The origin of the described mineral association is connected with (sub)recent weathering of primary ore minerals (tennantite, sphalerite, nickelskutterudite) in relatively dry conditions of abandoned mine adits.