ZANGBOITE, TiFeSi2, A NEW MINERAL SPECIES FROM LUOBUSHA, TIBET, CHINA, AND ITS CRYSTAL STRUCTURE

Abstract

We describe the new mineral species zangboite , ideally TiFeSi 2 , found in the podiform chromitites of the Luobusha ophiolite in Tibet, People’s Republic of China. The tabular to irregular crystals range from 0.002 to 0.15 mm in diameter and form an intergrowth with native silicon and a Fe–Si phase. Zangboite is steel grey in color. The luster is metallic, it is opaque, and the streak is black. The mineral is brittle; it has a conchoidal fracture and seems devoid of cleavage. The estimated Mohs hardness is 5½, and the calculated density is 5.09 g/cm 3 . The ideal composition is Ti 29.95, Fe 34.92, Si 35.13 wt%. Electron-microprobe analyses show traces of Cr, Mn, Zr and Al. The structure of zangboite has been refined by single-crystal X-ray diffraction to R 1 = 3.4%. The mineral is orthorhombic, space group Pbam ; its unit-cell parameters are a 8.6053(10), b 9.5211(11), c 7.6436(9) A, V 626.25(13) A 3 , Z = 12. The strongest five lines in the powder pattern [ d in A( hkl )(I/I 0 )] are: 2.1291(232)(100), 2.0251(042) (65), 2.2318(312)(50), 1.9155(004)(57), and 3.8358(002)(50). The mineral species and name were approved by the Commission on New Minerals, Nomenclature and Classification (IMA 2007–036).