Composition Silica Gneisses

201957gneissneiss pronounced "nice" is a metamorphic rock consisting mostly of quartz and feldspar and showing distinct layering or bandinghe layering of a gneiss may be weak or welldeveloped and consists of varying concentrations of biotite, garnet, hornblende, mica, and other mineralsese structures do not record a layered deposition process but arise from preferential.