STUDIES OF BRAZILIAN METEORITES XIV. MINERALOGY,PETROLOGY, AND CHEMISTRY OF THE CONQUISTA,MINAS GERAIS,CHONDRITE

The Conquista chondrite consists of major olivine, low-Ca pyroxene (both ortho- and twinned clino-), troilite and metallic nickel-iron; minor glassy to microcrystalline material and pigeonite; and accessory chromite, high-Ca clinopyroxene and hydrous ferric oxides that formed by terrestrial weathering of metallic nickel-iron. Results of microscopic, electron microprobe, and bulk chemical studies, particularly the compositions of olivine (Fa_17.2) and low-Ca pyroxene (Fs_15.4); the contents of metallic nickel-iron (18.5%) and total iron (25.83%); and the ratios of Fe°/Fe_total (0.64), Fe°/Ni° (9.59) and Fe_total/SiO₂ (0.69) indicate H-group classification. The pronounced, well-developed chondritic texture; the slight compositional variations in constituent phases; the high Ca contents of pyroxene and the presence of pigeonite, glassy to microcrystalline interstitial material rich in alkalis and SiO₂, and of twinned low-Ca clinopyroxene suggest that Conquista is of petrologic type 4.