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Orthocuproplatinum, Pt 3 Cu, a new mineral from the Lubero region, North Kivu, Democratic Republic of the Congo

par Cabral, Alexandre Raphael;Skála, Roman;Vymazalová, Anna;Maixner, Jaroslav;Stanley, Chris;Lehmann, Bernd;Jedwab, Jacques
Référence Mineralogy and petrology
Publication Publié, 2019

Article révisé par les pairs

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Résumé :

Orthocuproplatinum, Pt 3 Cu, 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, Pt 7 Cu. 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) Å; b = 5.4318(8) Å; c = 2.7502(4) Å; V = 114.74(3) Å 3 ; Z = 2. The calculated density is 17.866 g cm −3 . The strongest diffraction lines are [d in Å(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 243 kg mm −2 (VHN 25 ), corresponding to a Mohs hardness of 4. The empirical formula of orthocuproplatinum, calculated from a mean value of 12 electron-probe microanalyses that gave 12.9 wt% Cu and 87.3 wt% Pt, is Pt 2.76 Cu 1.24 on the basis of 4 atoms.