An account to igneous rocks Granite: Continental crust is mainly formed of this Ba rock. It is composed of quartz, feldspar, mica and ro homblende and the colour of this rock varies from white, grey to pink. This is an impermeable rock. Granite is m very much resistant to erosion as it is heavy and very hard. Granite is coarse granied as the magma is cooled and solidified very slowly in the earths interior (diameter >3 mm). Landforms developed on the regions of granite rock are generally rounded and domal.