O’Malley 017        30°32’41.2"S, 131°15’33.4"E

South Australia, Australia

Found: 10 Apr 2011

Classification: Ordinary chondrite (L6)

History: Three flat broken pieces found by E. Mare on the Nullarbor Plain.

Physical characteristics: Significantly weathered and without fusion crust.

Petrography: (E. Mare, Monash) Few indistinct chondrules (to 1 mm) in a heavily recrystallized matrix. Plagioclase to 100 μm. Chondrule types include CC and PO, however most are difficult to distinguish. Fe-Ni metal and troilite have been almost completely replaced by oxides, which comprise 3-5% of the meteorite. A large (7 mm) clast composed of olivine (~15%) and low-Ca pyroxene (~65%) phenocrysts (with minor Ca-pyroxene) in a groundmass (~20%) of plagioclase, skeletal olivine and chromite. Inside this clast there is no evidence for any metal or troilite having been present. Oxides occur along fractures in olivine and pyroxene grains. This clast has indistinct margins, indicating that it has been affected by metamorphism and is most likely to be an unusually large chondrule, rather than a breccia clast. Olivine grains have weak undulose extinction.

Geochemistry: (E. Mare, Monash) Microprobe analyses show that olivine and pyroxene compositions are uniform: olivine Fa_24.5-24.9, mean=24.74 mol%, std=0.15, n=10; Low-Ca pyroxene Fs_21.0-21.8, mean=21.25 mol%, std=0.27, n=7.

Classification: Ordinary chondrite (L6, S2, W4)