New kind of type 3 chondrite with a graphite-magnetite matrix

We have discovered four clasts in three ordinary-chondrite regolith breccias which are a new kind of type 3 chondrite. Like ordinary and carbonaceous type 3 chondrites, they have distinct chondrules, some of which contain glass, highly heterogeneous olivines and pyroxenes, and predominantly monoclinic low-Ca pyroxenes. But instead of the usual fine-grained, Fe-rich silicate matrix, the clasts have a matrix composed largely of aggregates of micron- and submicron-sized graphite and magnetite. The bulk compositions of the clasts as well as the types of chondrules (largely porphyritic) are typical of type 3 ordinary chondrites, although chondrules in the clasts are somewhat smaller (0.1–0.5 mm). A close relationship with ordinary chondrites is also indicated by the presence of similar graphite-magnetite aggregates in seven type 3 ordinary chondrites. This new kind of chondrite is probably the source of the abundant graphite-magnetite inclusions in ordinary-chondrite regolith breccias, and may be more common than indicated by the absence of whole meteorites made of chondrules and graphite-magnetite.