CAMERONITE, Cu5−x(Cu,Ag)3+xTe10(x= 0.43), FROM THE GOOD HOPE MINE, VULCAN, COLORADO: CRYSTAL STRUCTURE AND REVISION OF THE CHEMICAL FORMULA

Abstract

The crystal structure of the mineral cameronite, a rare copper-silver telluride, was solved using intensity data collected from a crystal of the holotype material from the Good Hope mine, Vulcan, Colorado (USA). The study revealed that the structure is monoclinic, space group C 2/ c , with cell parameters: a 17.906(1), b 17.927(1), c 21.230(2) A, β 98.081(8)°, and V 6747.2(8) A 3 . The refinement of an anisotropic model led to an R index of 0.0216 for 9688 independent reflections. Nineteen Te sites and 14 metal (M) sites occur in the crystal structure of cameronite. Six M sites host Cu with variable amounts of Ag, whereas the remaining eight M sites host Cu only. All of the atoms are in tetrahedral coordination and complex MTe 4 , M(Te 3 M), M(Te 2 M 2 ), TeM 4 , Te(M 3 Te), Te(M 2 Te 2 ), Te(MTe 3 ), and TeTe 4 crystal-chemical environments are formed, as is typical of many intermetallic compounds. The short bond distances observed mainly among the Te atoms are discussed in relation to other copper and silver tellurides and pure metals. Electron microprobe analyses of the crystal used for the structural study led to the formula Cu 7.08 Ag 1.06 Fe 0.01 S 0.01 Te 9.84 , on the basis of 18 atoms. On the basis of information gained from the structural and chemical characterization, the crystal-chemical formula was revised, yielding Cu 5− x (Cu,Ag) 3+ x Te 10 ( Z 14) with x = 0.43 instead of Cu 7 AgTe 10 ( Z 16) as previously reported.