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Klajite, MnCu4(AsO4)2(AsO3OH)2(H2O)10, from Jáchymov (Czech Republic): the second world occurrence

Published online by Cambridge University Press:  05 July 2018

J. Plášil*
Affiliation:
Institute of Physics ASCR, v.v.i., Na Slovance 2, Prague 8, 182 21, Czech Republic
A. V. Kasatkin
Affiliation:
V/O "Almazjuvelirexport", Ostozhenka str., 22, block 1, 119034 Moscow, Russia
R. Škoda
Affiliation:
Department of Geological Sciences, Masaryk University, Kotlářská 2, Brno, 611 37, Czech Republic
P. Škácha
Affiliation:
Mining Museum Příbram, Hynka Kličky Place 293, 261 01, Příbram VI – Březové Hory, Czech Republic Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University in Prague, Albertov 6, 128 43, Prague 2, Czech Republic
*
*E-mail: plasil@fzu.cz

Abstract

Klajite, MnCu4(AsO4)2(AsO3OH)2(H2O)10, the Mn-Cu-bearing member of the lindackerite group, was found in Jáchymov, Czech Republic, as the second world occurrence. It is associated with ondrušite and other arsenate minerals growing on the quartz gangue with disseminated primary sulfides, namely tennantite and chalcopyrite. Electron-microprobe data showed klajite aggregates to be chemically inhomogeneous at larger scales, varying from Mn-Ca-rich to Cu-rich domains. The chemical composition of the the Mn-rich parts of aggregates can be expressed by the empirical formula (Mn0.46Ca0.22Cu0.07Mg0.02)∑0.77(Cu3.82Mg0.14Ca0.03Zn0.01)∑4.00(As1.94Si0.06)∑2.00O8[AsO2.73(OH)1.27]2(H2O)10 (mean of seven representative spots; calculated on the basis of As + Si + P = 4 a.p.f.u. (atoms per formula unit) and 10 H2O from ideal stoichiometry), showing a slight cationic deficiency at the key Me-site. According to single-crystal X-ray diffraction, klajite from Jáchymov is triclinic, P, with a = 6.4298(8), b = 7.9716(8), c = 10.707(2) Å, α = 85.737(12)°, β = 80.994(13)°, γ = 84.982(10)°, and V = 538.85(14) Å3, Z = 1. The crystal structure was refined to R1 = 0.0628 for 1034 unique observed reflections (with Iobs > 3σ(I)), confirming that klajite (Mn-Cu member) and ondrušite (Ca-Cu member) are isostructural. The current data-set allowed determination of the positions of several hydrogen atoms. Discussion on hydrogen bonding networks in the structure of klajite as well as detailed bond-valence analysis are provided.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2014

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