Feldspar in Chondrites.
Whereas most chondrites contain sodic plagioclase (or occasionally maskelynite, its glassy equivalent), a few are free of feldspar. Absence of plagioclase is correlated with the presence of calcium-poor clinopyroxene (pigeonite sensu lato) instead of orthopyroxene. Olivine in feldspar-free chondrites is frequently variable in composition; in feldspar-bearing chondrites this mineral has essentially uniform composition. It appears that the silicate material of most chondrites was initially an association of olivine and pigeonite (or perhaps olivine and glass), and recrystallization has produced the usual olivine-orthopyroxene-sodic plagioclase association.
Mason
B
B