Published:January 01, 1972
The spherulitic and variolitic textures of Apollo 12 samples 12063 and 12065, the order of crystallization of all phases, the compositional trends and sector-zoning of the pyroxenes, the chrome partition between phases, the occurrences of metastable minerals, and the wide variations of edge compositions of the olivine and pyroxene suggest that essentially all the crystallization of both rocks took place under highly supercooled conditions at or near the lunar surface. The composition of the original magmas after nucleation of pyroxene and olivine approached those of the present rocks.
The abundance of calcium in olivine from 14 equilibrated low-iron chondrites was determined by microprobe analysis. With two exceptions (Shaw and Kunashak), median CaO abundances fall between 0.03 and 0.06 wt percent, substantially lower than those encountered in type 3 chondrites (for example, 0.15 percent in Sharps). It appears that much of the calcium in type 3 olivine was expelled during the metamorphic transition from type 3 to type 4. By contrast, changes from type 4 to type 6 were modest, though the data suggest slight calcium depletion in this interval.
High CaO contents (0.09 and 0.07 percent) in the Kunashak and Shaw chondrites, both type 6, suggest unusual thermal histories for these meteorites: shock reheating in the former case, and unusually high metamorphic temperatures in the latter.