New chemical and physical data on keilite from the Zaklodzie enstatite achondrite

Abstract

Keilite, (Fe,Mn,Mg,Ca,Cr)S, from the Zakłodzie enstatite achondrite is described. Forming xenomorphic grains up to 0.5 mm in diameter, the keilite is associated with troilite (or pyrrhotite), Fe-Ni metal, an (Fe,Zn,Mn)S phase, enstatite (with relict forsterite in cores), plagioclase and accessory schreibersite, oldhamite, graphite, sinoite, and an SiO 2 polymorph. It is brittle and possesses a good cleavage similar to that of galena, parallel to (001), (010), and (100). X-ray diffraction structural data reveal the following: cubic space group Fm3m, α = β = γ = 90°, a = 5.1717 (18) Å, unit-cell volume V = 138.32 (8) Å 3 ; D = 3.958 g/cm 3 ; Z = 4. The chemical formula based on 63 electron microprobe point analyses is: (Fe 0.437 , Mn 0.356 , Mg 0.160 , Ca 0.017 , Cr 0.019 , Zn 0.001 )S 1.008 . Compared with previously described keilites from enstatite chondrites, the Zakłodzie keilite is richer in (Mn,Ca,Cr)S and poorer in the Fe- and Mg-end-members and, consequently, it is nearer to alabandite and oldhamite. This is the first detailed description of keilite from a meteorite that is not an enstatite chondrite.