Unusual olivine and pyroxene composition in interplanetary dust and unequilibrated ordinary chondrites

Abstract

CHONDRITIC porous interplanetary dust particles (IDPs) collected in the stratosphere are considered to be micrometeoritic material different from any class of meteorites because of their fine-grained textures and high porosities¹. Several authors have suggested that chondritic porous IDPs might be cometary dust². Here we report the presence, in both a number of IDPs and in meteorite matrices, of olivine and orthopyroxene grains, low in FeO, but containing up to 5 wt% MnO. The majority of olivines and pyroxenes in meteorites contain less than 0.5 wt% MnO. The presence of these low-iron, manganese-enriched (LIME) olivines and pyroxenes in IDPs and meteorites may indicate a link between the origin and history of IDPs and the matrix material of primitive meteorites. The origin of the LIME silicates could be explained by condensation from a gas of solar composition. Forsterite is the first major silicate phase to condense from a solar nebula gas, and Mn, which is not stable as a metal under solar nebula conditions, would condense at ∼1,100K as Mn₂SiO₄ in solid solution with forsterite^3,4.