Dhofar 225

Oman

Found 2001 January 15

Carbonaceous chondrite (CM, anomalous)

A black stone weighing 90 g was found in the Dhofar region in Oman. Mineralogy and classification (M. A. Ivanova and M. A. Nazarov, Vernad; L. Taylor and A. Patchen, UTenn): fusion crust is distinct and black. Texturally the sample is similar to CM chondrites, consisting of fine-grained matrix, calcium-aluminum-rich inclusions (CAIs), irregularly-shaped olivine aggregates, and rare type I and II chondrules. Coarse-grained objects are surrounded by accretionary dust mantles. CAIs are mainly spinel-rich with perovskite, Al-diopside and forsterite surrounded by phyllosilicates; chondrules consist of olivine, very rare orthopyroxene embedded in completely altered mesostasis; type I chondrules and olivine aggregates contain kamacite blebs in forsterite; groundmass consists of phyllosilicates, isolated olivine grains (forsterite is dominant). Contains Ni-rich metal grains (up to 60 wt% of Ni), schreibersite, Ca-phosphates, sulfides (mostly pentlandite and pyrrhotite), chromite and escolaite; bulk chemistry: Fe/Si = 1.24, Mg/Si = 0.91, Al/Si = 0.093, low H₂O contents.  Oxygen isotopic composition (R. N. Clayton, UChi): δ^₁₈O = +21.85‰, δ^₁₇O = +9.22‰. The oxygen isotopic composition, low Fe/Si ratio and low H₂O content are atypical for CM chondrites. Specimens: type specimen, 19.7 g and two thin sections, Vernad; main mass is with the anonymous finder.