Granite is a coarse -grained intrusive igneous rock composed of quartz, alkali feldspar and plagioclase. It forms from magm with a high content of silica and alkali metal oxides that slowly cools and solidifies underground. it is common in the continental crust of earth, where it is found in igneous intrusions. These range in size fron dikes only a few centimeters across to batholiths exposed over hundreds of square kilometers.