Brownleeite; a new manganese silicide mineral in an interplanetary dust particle
Brownleeite; a new manganese silicide mineral in an interplanetary dust particle
American Mineralogist (February 2010) 95 (2-3): 221-228
Brownleeite, ideally stoichiometric MnSi, is a manganese silicide not previously observed in nature that was discovered within an interplanetary dust particle that likely originated from a comet. Three submicrometer brownleeite grains were found, with one of them poikilitically enclosed by Mn-bearing forsterite. Owing to the small size of the brownleeite grains, it was not possible to determine conventional macroscopic properties of this mineral; however, the chemical composition and crystal structure were well constrained by extensive quantitative energy dispersive X-ray analysis and electron diffraction using transmission electron microscopy (TEM). The crystal system for brownleeite is cubic (a = 4.557 Aa) with space group P2 (sub 1) 3, cell volume = 94.63 Aa (super 3) , Z = 4, density (calculated) = 2.913 g/cm (super 3) , and empirical formula: (Mn (sub 0.77) Fe (sub 0.18) Cr (sub 0.05) )Si. These brownleeite grains likely formed as high-temperature condensates either in the early Solar System or in the outflow of an evolved star or supernova explosion.