Příspěvek k chemickému složení minerálů skupiny pearceit-polybazit z Vrančic u Příbrami (Česká republika)
Jiří Litochleb, Petr Pauliš, Jiří Sejkora, František Novák
Three members of pearceite-polybasite group were found in samples from the Pošepný vein, Alexandr mine, Vrančice near Příbram, central Bohemia (Czech Republic). Polybasite forms there well-developed greyish-black pseudohexagonal tabular crystals up to 3 - 6 mm in size in cavities of calcite-quartz-chalcopyrite gangue in association with galena, sphalerite, hematite, tetrahedrite, pyrite and silver. Cupropearceite and cupropolybasite were identified as part of oscillatory zoned greyish-black pseudohexagonal tabular crystals up to 3 mm in cavities of calcite gangue in association with chalcocite, stromeyerite and bornite. The representative chemical analysis for all described minerals and comparison with published date are given. The high copper contents up to 6.84 apfu were determined in a part of analyses of cupropearceite indicating that in the structure module [M6T2S7]2- the M-position is fully occupied by Cu atoms. Regular minority contents of chlorine (0.03 - 0.07 apfu) in all studied samples from Vrančice are also interesting, up to now presence of chlorine was not described in the minerals of this group.