New igneous rocks are formed every day as magma or lava cools. All rocks originally come from igneous rock. When magma cools deep within the earth, it does so very slowly because it is not exposed to cool temperatures. Slow cooloing allows large crystals to develop in the rock. Rocks that form benearth the earth's surface, with either small or large crystals have a coarse texture and are known as intrusive igneous rock.
Granite is a common intrusive igneous rock.
Lava cools very quickly on the earth's surface because it is suddenly exposed to cool temperatures. Crystals often do not have time to develop in the rock that forms. Rock that forms without crystals on the earth's surface has a fine texture, and is called extrusive igneous rock. The most common rock formed from lava is called basalt. Igneous rock contains metallic minerals such as nickel, copper, gold and silver.