2007/12/01 by L. Bindi, M. Evain, P. G. Spry +2
paper · doi:10.1180/minmag.2007.071.6.641
crossref issued 2007/12/01 · crossref published 2007/12/01 · crossref published-print 2007/12/01 · crossref created 2008/07/17 · crossref published-online 2018/07/05 · crossref deposited 2021/02/13 · crossref indexed 2026/07/30
Abstract The pearceite-polybasite group of minerals, general formula [M 6 T 2 S 7 ][Ag 9 CuS 4 ] with M = Ag, Cu; and T = As, Sb, show a crystal structure which can be described as the succession, along the c axis, of two pseudo-layer modules: a [M 6 T 2 S 7 ] 2– A module layer and a [Ag 9 CuS 4 ] 2+ B module layer. Copper is present in one structural position of the B module layer and replaces Ag in the only fully occupied M position of the A module layer. When the Cu content is >4.00 a.p.f.u., the structural position of the A module layer becomes Cu-dominant and, consequently, the mineral deserves its own name. In this paper we report the crystal-chemical characterization of two Cu-rich members exhibiting the 111 unitcell type (corresponding to the Tac polytype). One sample (space group ( P ) m 1, a 7.3218(8), c 11.8877(13) Å, V 551.90(10) Å 3 , Z = 1) having As >Sb and with the structural position of the A module layer dominated by Cu, has been named cupropearceite and the other sample (space group (P3̄)m1, a 7.3277(3), c 11.7752(6) Å, V 547.56(8) Å 3 , Z = 1) having Sb >As has been named cupropolybasite. Both the new minerals and mineral names have been approved by the IMA-CNMNC.