The new mineral insizwaite (PtBi2) and new data on niggliite (PtSn)

Abstract

SummaryInsizwaite from Waterfall Gorge, Insizwa, is a new mineral with the composition Pt1·00Bi1·35Sb0·57. The name is for the locality and is to be applied to the end member PtBi2. The analysed material is an antimonian variety. The mineral is cubic, the unit-cell for the antimonian variety has a 6·625 (2) Å, probable space group Pa3, calc. D 12·8 g/cm3. The strongest lines on the X-ray diffraction powder pattern are: 2·96 (8) 210; 2·70 (8) 211; 2·34 (5) 220; 1·99 (10 311; 1·774 (7) 321; 1·433 (5) 421; 1·277 (6) 511, 333; 1·171 (6) 440; and 0·862 (7) 731. Under reflected light the mineral is white (in air and in oil) and is isotropic. Reflectance measurements at 470, 546, 589, and 650 nm gave 61·1, 60·0, 60·6, and 61·7 %. Micro-indentation hardness values range from 488 to 540 (av. 519) kg/mm2 with a 25 g load.New data are presented for niggliite from the type locality and for synthetic PtSn.