Kusachiite, CuBi 2 O 4 , a new mineral from Fuka, Okayama Prefecture, Japan

Abstract

Kusachiite, CuBi 2 O 4 , has been found in a calcite vein cutting gehlenite-spurrite skarns at Fuka, Okayama Prefecture. It is associated with calcite, henmilite, sillenite, bakerite, tenolite, bultfonteinite, apophyllite, cuspidine and thaumasite. Kusachiite occurs as prismatic crystals or globular aggregates of platy crystals. It is black, opaque with a metallic lustre. Kusachiite is tetragonal with space group P 4/ ncc, a = 8.511(2), c = 5.823(2) Å, Z = 4. The strongest lines in the X-ray powder pattern [ d in Å (I)(hkl)] are 3.191 (100)(211), 2.695 (18)(310), 1.947 (18)(411), 4.26 (17)(200), 2.913 (16)(002), 2.404 (13)(202), 1.728 (12)(213), and 1.652 (9)(332). The Mohs hardness is 4.5, and the density is 8.5(3) g/cm 3 (meas.) and 8.64 g/cm 3 (calc.). Cleavage is perfect on {110}. Six electron probe analyses gave the following mean values CuO 13.91, Bi 2 O 3 86.00 and total 99.91 in wt.%. The empirical formula calculated on the basis of O = 4 is Cu 0.960 Bi 2.027 O 4 with the simplified formula CuBi 2 O 4 .