IMA 2020–032 = krupičkaite

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Marco E. Ciriotti
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IMA 2020–032 = krupičkaite

Messaggio da Marco E. Ciriotti » gio 08 apr, 2021 14:43

Referenza:
▪ Steciuk, G., Sejkora, J., Čejka, J., Plášil, J., Hloušek, J. (2021): Krupičkaite, Cu6[AsO3(OH)]6·8H2O, a new copper arsenate mineral from Jáchymov (Czech Republic). Journal of Geosciences, 66, 37-50.

Abstract:
Krupičkaite, ideally Cu6[AsO3(OH)]6·8H2O, is a new supergene mineral from the Rovnost I shaft in Jáchymov, Czech Republic. It forms aggregates of pale bluish-green color and grows along with supergene minerals crystallizing on the strongly altered relics of massive tennantite, Bi-rich tennantite, galena, chalcopyrite, bornite, and chalcocite with disseminated uraninite in quartz. For a long time, krupičkaite has been left out due to its quite inconspicuous ap¬pearance that can be mistakenly referred to as geminite. At the ambient temperature, krupičkaite is monoclinic, a = 15.504(7) Å, b = 18.144(7) Å, c = 10.563(5) Å, β = 103.30(4)°, V = 2891.5(2) Å3, Z = 4, space group P21/m. Its structure has been solved and refined from 3D electron diffraction and further studied by Raman spectroscopy. The layered structure is built upon the alternation of two different cooper-arsenate sheets stacked along b presenting a characteristic wave shape along the a-axis and separated by a thick interlayer with channels containing only H2O. The collapsed chains of cooper polyhedra are connected the same way as in geminite through AsO4 tetrahedra. Krupičkaite joins the family of cooper arsenate minerals with which it shares structural similarities at the level of the As-Cu layers with the lindackerite supergroup, slavkovite, or yvonite.  

Overview of related layered cooper-arsenate minerals
Mineral Composition As/Cu (overall) As/Cu (As–Cu layer) As–Cu (layer) Interlayer
Krupičkaite Cu6[AsO3(OH)]6·8H2O 1 1 Chain 1: CuΦ5 and CuΦ6; Chain 2: CuΦ6 H2O
Geminite Cu(AsO3OH)·H2O 1 1 Layer 1: CuΦ5 and CuΦ6; Layer2: CuΦ6 H2O
Slavkovite Cu13(AsO4)6(AsO3OH)4·23H2O 1.3 1.1 CuΦ5 and CuΦ6 CuΦ4 and H2O
Ondrušite CaCu4(AsO4)2(AsO3OH)2·10H2O 1 1 CuΦ5 and CuΦ6 CaΦ6 and H2O
Lindackerite CuCu4(AsO4)2(AsO3OH)2·9H2O 1.25 1 CuΦ5 and CuΦ6 CuΦ6 and H2O
Yvonite Cu[AsO3(OH)]·2H2O 1 1 CuΦ4 H2O
Marco E. Ciriotti

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