Chondrules and other components in C, O, and E chondrites: Similarities in their properties and origins

Abstract

We describe three types of chondrules that are common to H3, LL3, CM2, CO3, and CV3 chondrites. Low and high‐FeO, porphyritic olivine chondrules contain olivine with Fa0.3–8 and Fa5–50 respectively, and can easily be distinguished petrographically. Poikilitic pyroxene chondrules have 1–20 vol % olivine (Fa0.2–8) enclosed by low‐Ca pyroxene (Fs0.5–7), and also occur in E chondrites. These three types formed in separate nebular regions which had dimensions and spacings such that a few percent of the chondrules that collided to form compound chondrules were of different types. Sorting of chondrule precursor material and mixing of chondrule types probably account for most variations in bulk and mineral chemistry among chondrite groups. Metallic Fe,Ni grains containing 0.1–1% Cr, Si, and P are present in low‐FeO olivine chondrules from all type 2 and least metamorphosed type 3 chondrites. Metal compositions reflect reduction during chondrule formation in the nebula, not nebular condensation. Opaque matrices in type 3 ordinary and carbonaceous chondrites are somewhat similar in composition and mineralogy, and probably have related origins. We conclude that chondrules in all known chondrite groups share similar nebular origins.