THE ORO GRANDE,NEW MEXICO,CHONDRITE AND ITS LITHIC INCLUSION

The Oro Grande, New Mexico, U.S.A., chondrite was found in 1971. Electron microprobe analyses and microscopic examination show the following mineralogy: olivine (Fa 19.3 mole percent), orthopyroxene (Fs 16.2 mole percent), diopside, feldspar (An 13.6 mole percent), chlorapatite, whitlockite, kamacite, taenite, troilite, chromite, and an iron-bearing terrestrial weathering product. A bulk chemical analysis of the meteorite shows the following results (weight percent): Fe 0.84, Ni 1.46, Co 0.07, FeS 3.62, SiO₂ 34.18, TiO₂ 0.14, Al₂O₃ 1.83, Cr₂O₃ 0.55, Fe₂O₃ 21.25, FeO 9.13, MnO 0.31, MgO 21.52, CaO 1.72, Na₂O 0.70, K₂O 0.08, P₂O₅ 0.25, H₂O+ 2.14, H₂O^- 0.40, C 0.22, Sum 100.41. On the basis of composition and texture, the Oro Grande meteorite is classified as an H5 chondrite. A large lithic fragment (～5 mm long) with a very fine-grained texture different from that of the host meteorite was analyzed for bulk composition using the broad beam of an electron microprobe, and was found to be enriched in Ca, Al, Na, and K, and depleted in Mg and Fe relative to the bulk composition of the host meteorite. Its mineral compositions, however, are very similar to those of the host. It is suggested that the fragment is not a xenolith of a previously undescribed type of achondrite, but is probably an impact-produced partial melt of the host chondrite or a fragment of an unusually large chondrule.