Mineralogy and chemistry of the carbonaceous chondrite PCA 91467 (CH)

Details Mineralogy and chemistry of the carbonaceous chondrite PCA 91467 (CH) Mineralogy and chemistry of the carbonaceous chondrite PCA 91467 (CH)

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.444b&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 444

Mathematics

Logic

2

Abundance, Breccia, Carbonaceous Chondrites, Chemical Composition, Meteoritic Composition, Mineralogy, Chondrule, Inclusions, Metallicity, Meteoritic Microstructures, Olivine

Scientific paper

The two carbonaceous chondrites ALH 85085 and Acfer 182 have distinct mineralogical and chemical similarities. Due to their high bulk Fe content and metal abundance they were designated as CH chondrites. Meanwhile, two other (probably unpaired) meteorites have been recognized as belonging to this new group of carbonaceous chondrites. In this study we report on the mineralogy and chemistry of PCA 91467, the largest collected piece of the PCA 91328 chondrite. In its interior PCA 91467 is quite fresh with only negligible amounts of terrestrial weathering products. Like ALH 85085 and Acfer 182, this chondrite is metal rich and has only a small fraction of chondrules. The most abundant components are mineral and lithic (often cryptocrystalline) fragments. Also, Ca, Al-rich inclusions (CAIs) and dark inclusions are embedded in a fine-grained, clastic matrix, which is highly cemented (low porosity). PCA 91467 is a breccia. Considering the chondrules, a high abundance of cryptocrystalline chondrules (less than 160 microns) exists in PCA 91467, also typical of ALH 85085 and Acfer 182. The PCA 91467 meteorite has similar unique chemical signatures to the two other CH chondrites. The total Fe content of PCA 91467 is 37.42 wt%, between that of Acfer 182 (34.87 wt%) and ALH 85085 (39.83 wt%). In addition, all siderophile elements are enhanced, together with Fe and similar to the other two CH meteorites. PCA 91467 is in many respects more similar to ALH 85085 than to Acfer 182. The chemical characteristics of PCA 91467, Acfer 182, and ALH 85085 suggest that these meteorites form a unique group of carbonaceous chondrites as suggested by Bischoff et al. The large excess in metallic Fe and associated elements documents larger metal-silicate fractionations in the solar nebula than previously observed.

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