Sayh Al Uhaymir 085, Cv3 Chondrite: Mineralogical Links with Ck Chondrites

Sayh al Uhaymir 085 is similar to CV3 carbona-ceous chondrites of the oxidized subgroup, and it has some peculiarities and characteristics of CK chondrites. We report on the petrography, mineral chemistry, and oxygen isotopic compositions of Sayh al Uhaymir 085, and discuss its peculiarities and origin. Petrography and mineral chemistry. Sayh al Uhaymir (SaU) 085, a 112 g carbonaceous chondrite, was found in the desert of Oman on January 11, 2002. It is a black stone with a distinct fusion crust. In general, textures of SaU 085 are similar to those of CV3-chondrites, but the meteorite demonstrates some interesting unusual features. In SaU 085, the matrix /(chondrule+aggregates) ratio is 0.77, similar to Allende and Mokoia, both oxidized CV chondrites, but also similar to the reduced CV chon-drites [1]. This ratio differs from some other members of the oxidized subgroup (1.2, in Kaba, Bali, and Groznaya). Only two chondrules, 0.2 and 1.4 mm in size, were found, which is very unusual for CV chondrites. They are of the porphyritic olivine-and pyroxene-rich (POP) textural type, both of type II. They contain magnetite and minor kamacite. Olivine and pyroxene are the dominant mineral phases in olivine aggregates; sulfide, spinel, chromite, and magnetite are accessory phases. The chondrule and aggregate mesostasis is completely altered , and no primary glass or plagioclase were found. An unusual characteristic of SaU 085 is the presence of magnetite masses in the olivine aggregates. These magnetite objects, 20-100 µm in size, consist of Cr-rich magnetite with small kamacite inclusions, rare sulfides embedded in a matrix of fayalitic olivine, with traces of cronstedtite, and altered material. Two fine-grained CAIs, 1 x 1 and 1.8 x 1.9 mm in size, were found in an SaU 085 section. They have a concentrically zoned structure and consist of spinel, melilite, anorthite, Al-diopside, forsterite, minor kama-cite, and magnetite. The CAIs have undergone weak alteration, and rare nepheline and sodalite occur. The matrix of SaU 085 contains fragments of FeO-rich olivine, pyroxene, magnetite, spinel, chromite, sulfides, and rare Fe metal. It also contains phyllosili-cates, and in general, the intensity of the matrix alteration is similar to that in the Mocoia and Bali matrices. Olivine compositions from chondrules and aggregates are in the range of those in CV chondrites, Fa 0.7-45%. In the rims of the CAIs, as well as in most aggregates , the olivine is forsteritic and shows limited zoning in FeO. Olivine contents …