Linzhiite, FeSi2, a redefined and revalidated new mineral species from Luobusha, Tibet, China

Abstract

“Ferdisilicite” (FeSi 2 ) was first described as a member of the Fe–Si alloy mineral series by Gevork’yan (1969), without CNMMN approval. It is redefined here as a new mineral, revalidated with the new name linzhiite with a CNMNC approval (IMA 2010-011). The type sample was found in a podiform chromitite from the Luobusha ophiolite in Tibet, People’s Republic of China. It occurs as irregular grains ranging from 0.04 to 0.5 mm in diameter and intergrowths with zangboite and native silicon. Linzhiite is steel grey in colour, opaque, with a metallic lustre and a greyish-black streak. The mineral is brittle and has a conchoidal fracture. Cleavage was not observed. The Mohs hardness is 6½, and the calculated density is 4.972 g/cm 3 . Reflectance values of the material in air ( R %) are: 26.3 at 470 nm, 30.3 at 546 nm, 32.9 at 589 nm, and 36.3 at 650 nm. The composition (mean of 12 EMP analyses) is Fe 49.09, Si 50.00, Al 0.64 and Mn 0.28 wt%, sum 100.01 wt%. The ideal formula is FeSi 2 . The crystal structure was refined from single-crystal X-ray diffraction data to R = 0.043. The mineral has a tetragonal P 4/ mmm structure, with a = 2.696 (1) A, b = 2.696 (1) A, c = 5.147 (6), V = 37.41 (14) A 3 , Z = 1. The five strongest X-ray powder diffraction lines [ d -spacing in A ( I / I 0 )] are: 5.136 (96), 2.374 (81), 1.896 (55), 1.849 (100), and 1.086 (36). Linzhiite formed in a strongly reducing environment and possibly occurs as xenocrysts derived from mantle sources.