BH250-183
Title
Subject
Description
Minor Minerals: muscovite, chlorite
BH250-183 was collected during an Alumina field trip to Tanzania. The sample lies near the western margin of the Archean–Proterozoic Tanzanian Craton, which hosts ancient metamorphic basement rocks.
Textures include, recrystallized quartz grains with subgrain boundaries and irregular grain-shape mosaics with crystalloblastic, foliated fabric — microscopic evidence of intense deformation (SpringerLink). In some areas, quartz grains can be coarse, reaching 1–2 cm in diameter.
It is a metamorphic quartzite or vein quartz formed during Pan-African orogenic events, characterized by very high quartz purity, deformation and recrystallization textures, and typical granulite-facies remodeling features.
Muscovite grains are aligned in a foliation throughout the thin sections. Muscovite in metamorphosed quartzite commonly forms from the metamorphism of clays (kaolinite, illite) originally present in the sandstone’s cement or matrix. This suggests that clay mineral cements were present before metamorphism, acting as a binding material between quartz grains, and transformed during burial to amphibolite facies conditions.
Coverage
GPS Coordinates: 1°51'51"S, 35°16'42"E