Makroskopický covellin z rudního revíru Krupka v Krušných horách (Česká republika)

Pages 31-34
Bulletin mineralogicko-petrologického oddělení Národního muzea v Praze | 2009/17/2

Megascopic aggregates of covellite were found at thin vein in the old Martin gallery, the Krupka ore district, the Krušné hory Mountains, Czech Republic. Covellite forms abundant grains 0.1 - 2 mm in size in association with amorphous Fe-As-Si-O phase, tennantite and rare brochantite. It is opaque, dark indigo blue to dark purple with intense metallic luster and perfect cleavage. Covellite from Krupka is hexagonal, space group P63/mmc, the unit-cell parameters refined from X-ray powder data are: a = 3.794(2), c = 16.39(1) Å and V = 203.9(2) Å3. Chemical analyses yielded average composition Ag 0.83, Zn 0.03, Cu 65.16, Sb 0.02, S 33.05, total 99.08 wt. %, corresponding to (Cu0.99Ag0.01)Σ1.00S1.00 on the basis of 2 apfu. Associated tennantite is Zn-dominant member with average composition Ag 0.13, Fe 0.40, Cd 0.21, Zn 8.27, Cu 42.44, Sb 0.02, Bi 0.07, As 19.66, S 28.08, total 99.28 wt. % and empirical formula (Cu9.97Ag0.02)Σ9.99(Zn1.89 Fe0.11Cd0.03)Σ2.03(As3.92Bi0.01)Σ3.93S13.07 on the basis 29 apfu. The origin of macroscopic covellite at Krupka is interpreted as product of weathering of primary tennantite in conditions of supergene enrichment.

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