Petrography and petrology of basaltic achondrite polymict breccias /Howardites/

The reported investigation is based on the results from petrographic observations, electron microprobe analyses of constituent phases, and defocused beam analyses of clasts and glasses. Howardites consist of mostly angular-to-rounded mineral, rock, and breccia clasts compacted in variable grain-sized matrices of finely comminuted materials. Attention is given to ophitic and subophitic rocks, granular basalts and microgabbros, mafic rocks, Al-rich rocks, breccia clasts, impact melt rocks, glasses, meteorite clasts, bulk composition, particle size distribution, howardite component composition, questions of breccia formation, and parent body implications. It is found that the four main rock types found in howardites do have certain analogies to lunar rocks. It is tempting to speculate that both the moon and the basaltic achondrite parent body formed similar rock suites in their evolutionary processes.