In the commercial stone industry a “granite” is a stone that is harder than marble. Under this definition gabbro, basalt, schist, gneiss, diorite and many other stones are referred to as “granite”.
True granites are typically light-colored igneous stones with grains large enough to be visible to the naked eye. It forms during slow crystallization of magma deep below the Earth's surface. Granite is composed mainly of quartz and feldspar with minor amounts of micas and other minerals. This composition usually gives granite a red, pink, gray or white color with dark mineral grains.