Barquillite, Cu-2(Cd, Fe)GeS4, a new mineral from the Barquilla deposit, Salamanca, Spain

Barquillite, ideally Cu-2(Cd, Fe)GeS4, is a new mineral species found in th e Barquilla Sn-Ge-Cd-Cu-Fe vein-type deposit, Salamanca, Spain. This minera l occurs as plates and rosette-like aggregates of thin platy crystals, less than 50 mu m in size. It is commonly in contact with terrahedrite and chal copypite, less so with bornite, mawsonite, stannite and stannoidite. Barqui llite is opaque, with a metallic luster. In reflected light, it has a grey colour with a violet tint, very weak pleochroism, very weak bireflectance, and is very weakly anisotropic. Reflectance spectra are given. The micro-in dentation hardness ranges between 180 and 300 kg/mm(2). The mean of thirty four analyses gives: Cu 30.67, Ag 0.26, Cd 20.38, Fe 2.20, Mn 0.43, Zn 0.09 ,Ge 14.99, Sn 0.17, Sb 0.09, Bi 0.16, Ga 0.05, S 29.42, a total of 98.91 wt .%, corresponding to: (Cu2.10Ag0.01)(Sigma 2.11) (Cd0.79Fe0.17Mn0.03Zn0.01) (Sigma 1.00)(Ge0.90Sn0.01)(Sigma 0.91) S-3.98 (on the basis of 8 atoms) or simply Cu-2(Cd, Fe)GeS4. Based on the empirical formula and Z = 2, D-calc = 4.53 g/cm(3). The X-ray powder diffraction pattern obtained is analogous t o that of briartite (JCPDS 25-282). The strongest X-ray powder diffraction lines are (d in Angstrom(I)(hkl)): 3.10(100)(112), 1.92(80)(220), 1.89(70)( 204), 1.64(60)(312), 1.60(20)(303, 116) and 2.73(10)(200). The refinement o f the lattice parameters leads to a = 5.45(4) Angstrom and c = 10.6(1) Angs trom, indexed by analogy to briartite. Barquillite is therefore a member of the stannite group. the Cd-dominant analogue of briartite. The name is giv en after the village of Barquilla, very near the type locality.