Igneous rocks are formed from the solidification of molten rock material. There are two basic types.
Intrusive igneous rocks crystallize below Earth’s surface, and the slow cooling that occurs there allows large crystals to form. Examples of intrusive igneous rocks are DIORITE, GABBRO, GRANITE, PEGMATITE, and PERIDOTITE.
Extrusive igneous rocks erupt onto the surface, where they cool quickly to form small crystals. Some cool so quickly that they form an amorphous glass. These rocks include andesite, basalt, obsidian, pumice, rhyolite, scoria, and tuff.
Granite is a light-colored IGNEOUS ROCK with grains large enough to be visible with the unaided eye. It forms from the slow crystallization of magma below Earth’s surface. Granite is composed mainly of quartz and feldspar with minor amounts of mica, amphiboles, and other minerals. This mineral composition usually gives granite a red, pink, gray, or white color with dark mineral grains visible throughout the rock.
Granite is the best-known igneous rock. Many people recognize granite because it is the most common igneous rock found at Earth’s surface and because granite is used to make many objects that we encounter in daily life. These include counter tops, floor tiles, paving stone, curbing, stair treads, building veneer, and cemetery monuments.