gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1975.040.311.03 Argentian Mercurian Tetrahedrite, a New Variety, from the Chiprovtsi Ore Deposit, Western Stara-Planina Mountains, Bulgaria Atanasov Vassil AT. Higher Institute of Mining and Geology, Sofia 56, Bulgaria 9 1975 40 311 233 237 15 7 1974 13 9 1974 Copyright © 1975, The Mineralogical Society 1975 Summary

An electron-probe microanalysis of tetrahedrite occurring together with the latest-deposited pyrite-cinnabar association in the Chiprovtsi lead-silver deposit yielded more than 16 wt. % Ag and more than 18 wt. % Hg. X-ray powder examination established an extremely large unit-cell edge, a 10·64±0·01 Å. Vickers microhardness 223 to 237 kg/mm2. The chemical formula derived on the basis of the analyses made is quite near to Cu6+(Cu+, Ag+)4(Hg,Zn)2(Sb,As)4S113. There is not any antiparallelism between Ag and Hg in tetrahedrite. The name proposed for all stages of simultancous isomorphic replacement along the Cu+-Ag+ and Cu2+-Hg2+(Zn2+,Fe2+) directions is argentian mercurian tetrahedrite. The upper limits of the Ag and Hg content are expected to be Cu6Ag4Hg2(Sb,As)4S13. It is the six copper atoms (Cu4+·Cu22+), sited in the Laves' polyhedra, that are replaced by Ag+ and Hg2+ respectively.