Orthocuproplatinum, Pt3Cu, a new mineral from the Lubero region, North Kivu, Democratic Republic of the Congo

摘要

Orthocuproplatinum, Pt3Cu, is a new mineral from the Lubero region of North Kivu, Democratic Republic of the Congo. The mineral, which has a synthetic analogue, occurs as a 1.5-mm-long alluvial grain in a heavy-mineral concentrate, together with the holotype specimen of kitagohaite, Pt7Cu. The grain of orthocuproplatinum has a rim of hongshiite, PtCu, and abundant inclusions of calcite. Opaque and metallic, orthocuproplatinum has a whitish colour in reflected light and slightly perceptible anisotropy. The crystal structure of orthocuproplatinum is orthorhombic, space group Cmmm. Its unit-cell parameters: a=7.681(1) angstrom; b=5.4318(8) angstrom; c=2.7502(4) angstrom; V=114.74(3) angstrom(3); Z=2. The calculated density is 17.866gcm(-3). The strongest diffraction lines are [d in angstrom(I)]: 2.337 (11), 2.236 (100), 2.217 (97), 1.932 (61), 1.920 (30), 1.362 (36), 1.169 (24), 1.161 (23). The Vickers hardness is 243kgmm(-2) (VHN25), corresponding to a Mohs hardness of 4. The empirical formula of orthocuproplatinum, calculated from a mean value of 12 electron-probe microanalyses that gave 12.9wt% Cu and 87.3wt% Pt, is Pt2.76Cu1.24 on the basis of 4 atoms.