Explanation: Gneiss is a metamorphic rock formed from shale at very high temperature and pressure condition. They exhibit a preferred alignment or orientation of platy minerals called foliation. They are coarse grained and exhibit gneissose banding. They are formed from highest grade regional metamorphism with temperature between 450 - 600 degree celcius and pressure between 800 - 1000 mega pascal. They generally occur in cores of fold mountain belts where mountain ranges have been eroded.
