Granite is an igneous rock that injects, or intrudes, as magma into Earth's crust and then cools. It consists of four main mineral compounds. Two of these are types of feldspar, a group of silica compounds that constitute the most abundant mineral group on Earth.ranite is an igneous rock that injects, or intrudes, as magma into Earth's crust and then cools. It consists of four main mineral compounds. Two of these are types of feldspar, a group of silica compounds that constitute the most abundant mineral group on Earth.