Igneous rocks are a type of rock formed from the cooling and solidification of magma or lava. They are classified according to their mineral composition and texture. Basalts, sials, simas, and granites are all examples of igneous rocks. Basalts are dark-colored, fine-grained rocks that form when molten lava cools quickly. Sials are light-colored, coarse-grained rocks that form when molten lava cools slowly. Simas are intermediate between basalts and sials. Granites are coarse-grained rocks composed of quartz, feldspar, and mica.