Krupičkaite, Cu6[AsO3(OH)]6·8H2O, a new copper arsenate mineral from Jáchymov (Czech Republic)
Gwladys Steciuk, J. Sejkora, Jiří Čejka, Jakub Plášil, Jan Hloušek
Abstract
Krupikaite, ideally Cu 6 [AsO 3 (OH)] 6 8H 2 O, is a new supergene mineral from the Rovnost I shaft in Jchymov, Czech Republic. It forms aggregates of pale greenish-blue 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, krupikaite has been left out due to its quite inconspicuous ap pearance that can be mistakenly referred to as geminite. At the ambient temperature, krupikaite is monoclinic, a = 15.504(7) , b = 18.144(7) , c = 10.563(5) , = 103.30(4), V = 2891.5(2) 3 , Z = 4, space group P2 1 /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 copper-arsenate sheets stacked along b presenting a characteristic wave shape along the a-axis and separated by a thick interlayer with channels containing only H 2 O. The collapsed chains of copper polyhedra are connected the same way as in geminite through AsO 4 tetrahedra. Krupikaite joins the family of copper arsenate minerals with which it shares structural similarities at the level of the As-Cu layers with the lindackerite supergroup, slavkovite, or yvonite.