WATANABEITE, CU-4(AS,SB)(2)S-5, A NEW MINERAL FROM THE TEINE MINE, SAPPORO, HOKKAIDO, JAPAN

Watanabeite Cu-4(As,Sb)(2)S-5, in which As>Sb, is a new copper sulphos alt that occurs with quartz in a hydrothermal vein at the Teine mine, Sapporo, Hokkaido, Japan. It is silvery lead-grey in colour with lead- grey streak. VHN100=253-306 kg/mm(2), brittle. It has no cleavage and the fracture is uneven. The measured density=4.66(2) g/cm(3) The mean of six microprobe analyses gave Cu 41.1, Ag 0.1, Mn 0.3, As 15.4, Sb 1 4.3, Bi 2.4, S 26.2, a total of 99.8 wt.%, corresponding to: (CU3.94Mn 0.03M Ag-0.01)(Sigma 3.98)(As1.25Sb0.72Bi0.07)(Sigma 2.04)S-4.98 (basi s: total atoms=11), or ideally, CU4(AS,Sb)(2)S-5, With AS>Sb. The X-ra y powder pattern resembles that of tetrahedrite but has subsidiary dif fractions and is similar to that of synthetic Cu24As12S31 (Maske and S kinner, 1971). It is indexed on an orthorhombic cell with a=14.51 Angs trom, b=13.30 Angstrom, c=17.96 Angstrom (all+/-0.01 Angstrom), and Z= 16. Calculated density is 4.66 g/cm(3). It is optically similar to tet rahedrite but is grey and weakly bireflectant. No internal reflections were observed. The maximum and minimum reflectance values in air and in oil (n(D)=1.515) for the COM wavelengths are: 470 nm-32.5, 31.5; 17 .7, 17.0, 546 nm-32.0, 31.1; 17.0, 16.3, 589 nm-31.1, 30.3; 16.1 m 15. 5, 650 nm-30.O, 29.3; 15.0, 14.5%, respectively. Watanabeite forms mas ses composed of aggregates of minute grains up to 50 mu m in diameter. Apart from some minute inclusions of emplectite, native bismuth and t ennantite, it is almost monominerallic.