|Publication Type:||Journal Article|
|Year of Publication:||2015|
|Authors:||Sejkora, J, Škácha, P, Dvořák, Z, Muzikant, P|
|Journal:||Bulletin mineralogicko-petrologického oddělení Národního muzea v Praze|
|Keywords:||chemical composition, Czech Republic, new mineral phases, olivenite, powder X-ray diffraction data, slavkovite, strashimirite, the Krupka ore district, unit-cell parameters|
A unique supergene mineral association was found at abandoned Gallery No. 3 Preisselberg, the Krupka ore district, Krušné hory Mountains, Czech Republic. Slavkovite forms there light pale blue to blue-green rosettes up to 1 mm across composed by lath-like crystals; it is translucent (in aggregates) to transparent (in crystals), very brittle, and has a vitreous luster and perfect cleavage. It is triclinic, space group P-1, the unit-cell parameters refined from X-ray powder diffraction data are: a 6.414(2), b 14.370(3), c 16.527(4) Å, α 102.81(2), β 101.12(2), γ 97.94° and V 1431.0(8) Å3; its chemical analyses correspond to the empirical formula (Cu12.92Zn0.05Al0.02)Σ12.99[(AsO4)6.01(PO4)0.01]Σ6.02(AsO3OH)3.98·23H2O on the basis As+P=10 apfu. Olivenite was found as relatively abundant dark olive green hemispherical to spherical aggregates up to several mm in size. It is orthorhombic, space group Pnnm, the unit-cell parameters refined from X-ray powder diffraction data are: a 8.6300(8), b 8.2405(8), c 5.8384(2) Å and V 422.31(5) Å3; its chemical analyses correspond to the empirical formula (Cu2.01Zn0.01Fe0.01)Σ2.03[(AsO4)0.99(PO4)0.01]Σ1.00(OH)1.06 on the basis As+P = 1 apfu. Abundant strashimirite occurs there as greenish to white coatings on the area to several cm2, its light green crystalline aggregates up to 0.5 mm in size consisting of acicular crystals are more rare. Strashimirite is probably monoclinic, space group P2, the unit-cell parameters refined from X-ray powder diffraction data are: a 9.569(6), b 18.59(1), c 9.032(6) Å, β 97.21(6)° and V 1594(1) Å3; its chemical analyses correspond to the empirical formula (Cu7.89Al0.07Zn0.05Ca0.03)Σ8.04 [(AsO4)3.74(SO4)0.24 (PO4)0.03]Σ4.00(OH)4.41·5H2O on the basis As+P+S = 4 apfu. Brochantite forms there abundant dark green fine crystalline coatings on the area up to several cm2 in size and rarely also dark green tiny (up to 0.5 mm) prismatic crystals. It is monoclinic, space group P21/a, the unit-cell parameters refined from X-ray powder diffraction data are: a 13.133(1), b 9.855(1), c 6.016(1) Å, β 103.25(1)° and V 757.8(1) Å3; its chemical analyses correspond to the empirical formula (Cu3.91Al0.02)Σ3.93[(SO4)0.97(AsO4)0.03]Σ1.00(OH)5.85 on the basis S+As+P = 1 apfu. Devilline was found as relatively abundant whitish fine crystalline coatings on the area up 1 x 1 cm in size; light bluish green aggregates up to 0.5 cm across or rarely also transparent tabular crystals up to 0.2 mm across. Devilline is monoclinic, space group P21/c, the unit-cell parameters refined from X-ray powder diffraction data are: a 20.86(1), b 6.195(3), c 21.96(1) Å, β 102.92(1)° and V 2767(3) Å3; its chemical analyses correspond to the empirical formula Ca1.05(Cu4.11Al0.02)Σ4.13(SO4)2.00(OH)6.39·3H2O on the basis S = 2 apfu. An unnamed Cu-Ca arsenate occurs there as lavendulan-like blue crystalline coatings covering area up to 5 x 5 mm in size or hemispherical aggregates up to 0.5 mm across; its aggregates are composed from very thin (only 1 - 4 μm) tabular crystals up to 80 μm in size. Its X-ray powder data (strongest line 12.51 Å) does not correspond to any known mineral phases. Chemical composition of this mineral phase is possible to be expressed on the basis As+P+S = 4 apfu by empirical formulae Na0.03Ca1.03(Cu4.99Al0.03Zn0.01)Σ5.03 [(AsO4)3.73(SO4)0.25(PO4)0.02]Σ4.00Cl0.43·nH2O (thin tabular aggregates) or (Na0.03K0.02)Σ0.16Ca1.17(Cu4.69Al0.03Zn0.01)Σ4.73[(AsO4)3.73(SO4)0.25(PO4)0.02]Σ4.00 Cl0.59·nH2O (tabular aggregates). Further an unnamed Cu arsenate forms there light pale bluish green crystalline aggregates up 1 - 2 mm in size composed by tabular crystals up to 250 μm across in association with slavkovite. It is transparent to translucent, has a vitreous luster and perfect cleavage. Its X-ray powder data (strongest line 9.807 Å) does not correspond to any known mineral phases. This mineral phase is considerably unstable under electron beam of EPMA, the cation/anion ratio determined from WDS is in the range of 1.16 - 1.36. The origin of described mineral association is connected with (sub)recent weathering of primary tennantite in conditions of abandoned mine adit. Origin of Cu-arsenates is possible to express by following sequence: strashimirite → Cu-Ca arsenate → olivenite → slavkovite → Cu-arsenate.
Slavkovit z Preisselbergu, rudní revír Krupka (Česká republika) a jeho minerální asociace