Electron and optical microscopy studies of extraterrestrial minerals in NWA4047 meteorite

Abstract

Analytical electron microscopy and optical microscopy were used to determine the elemental and mineral composition of NWA4047 meteorite. The meteorite was found in 2005 in Morocco, and in 2006 was preliminary classified as H4-5 ordinary chondrite. The main crystalline meteorite minerals: olivines, pyroxenes, kamacite and taenite, feldspars, as well as troilite identified in our sample represent extraterrestrial minerals typical of the ordinary chondrite of high iron content. Low-Ca orthopyroxene called bronzite has been revealed. Single enstatite and clinopyroxene crystals have also been identified. Olivines in the meteorite contain 18 mol % of fayalite. The meteorite is a monomict breccia, in which fragments of petrographic types 4, 5, and 6 are present, with the groundmass being type 4. Some of clasts contain large grains of feldspars and high content of feldspars, which is typical of petrologic type 6. Chemical and mineral composition, petrologic types of chondrules, their abundance and sizes, the presence of troilite-kamacite veins, and nonoxidised iron phases prove that the chondrite belong to H group, i.e. to the olivine-bronzite group. Our results show that the NWA4047 meteorite is H4-6 ordinary chondrite. The weathering grade of the meteorite W0/1 is the same as previously established, but the shock grade S3 seems to be higher in comparison with the previous classification.