Petrology of mare-type basalt clasts from consortium breccia 73255.

Breccia 73255 contains sparse small clasts of basalts that have mare affinities; the basalts are members of a single differentiated suite. The clasts have been fractured throughout and locally granulated. Textural and compositional evidence indicates that the fracturing and granulation were produced by the 73255 breccia-forming event, and this event took place before the basalts had completely solidified. Thus, it appears that the eruption of the basalts took place at about the same time as the formation of the 73255 breccia, about 3.9 b.y. ago. The mineral assemblages and modes of the basalt clasts are those typical of mare basalts, but the clasts are not identical in detail with any basalts returned from the mare surfaces. They are instead most similar to the 14053-type basalts from the Apollo 14 site.