Mineralogy and chemistry of Rumuruti: The first meteorite fall of the new R chondrite group

Details Mineralogy and chemistry of Rumuruti: The first meteorite fall of the new R chondrite group Mineralogy and chemistry of Rumuruti: The first meteorite fall of the new R chondrite group

Mar 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29..275s&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 2, p. 275-286

Mathematics

Logic

45

Chemical Composition, Chondrites, Meteoritic Composition, Meteoroid Showers, Mineralogy, Abundance, Breccia, Olivine, Oxygen Isotopes, Meteorites, Stony Meteorites, Chondrites, R Chondrites, Rumuruti, Mineralogy, Chemistry, Meteorite Fall, Description, Classification, Chemistry, Comparison, Abundance, Oxidation, Oxygen, Isotopes, Parent Bodies, Samples, Meteorite, Laboratory Studies, Procedure, Petrography, Electron Microscopy, Microprobe Methods, Data, Origin, Bse, Formation, Refractory Material, Lithophil

Scientific paper

The Rumuruti meteorite shower fell in Rumuruti, Kenya, on 1934 January 28 at 10:45 p.m. Rumuruti is an olivine-rich chondritic breccia with light-dark structure. Based on the coexistence of highly recrystallized fragments and unequilibrated components, Rumuruti is classified as a type 3-6 chondrite breccia. The most abundant phase of Rumuruti is olivine (mostly Fa(approximately 39) with about 70 vol%. Feldspar (approximately 14 vol%; mainly plagioclase), Ca-pyroxene (5 vol%), pyrrhotite (4.4 vol%), and pentlandite (3.6 vol%) are major constituents. All other phases have abundances below 1 vol%, including low-Ca pyroxene, chrome spinels, phosphates (chlorapatite and whitlockite), chalcopyrite, ilemenite, tridymite, Ni-rich and Ge-containing metals, kamacite, and various particles enriched in noble metals like Pt, Ir, and Au. The chemical composition of Rumuruti is chondritic. The depletion in refractory elements (Sc, REE, etc.) and the comparatively high Mn, Na, and K contents are characteristic of ordinary chondrites and distinguish Rumuruti from carbonaceous chondrites. However, S, Se, and Zn contents in Rumuruti are significantly above the level expected for ordinary chondrites. The oxygen isotope composition of Rumuruti is high in delta O-17 (5.52%) and delta O-18 (5.07%). With Rumuruti, nine meteorites samples exist that are chemically and mineralogically very similar. These meteorites are attributed to at least eight different fall events. It is proposed in this paper to call this group R chondrites (rumurutites) after the first and only fall among these meteorites. The meteorites have a close relationship to ordinary chondrites. However, they are more oxidized than any of the existing groups of ordinary chondrites. Small, but significant differences in chemical composition and in oxygen isotopes between R chondrites and ordinary chondrites exclude formation of R chondrites from ordinary chondrites by oxidation. This implies a separate, independent R chondrite parent body.

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