Igneous Rocks

Igneous rocks form by the cooling and crystallization of molten rock and are often characterized by their random interlocking crystals. Cooling may take place very slowly deep below the Earth's surface, resulting in large mineral crystals (like those shown in the sample of granite at the right) - producing "intrusive" igneous rocks. Alternatively, cooling of the molten rock may take place fairly rapidly at/near the Earth's surface, resulting in mineral crystals that are much smaller (generally too small to see with the unaided eye) - producing "extrusive" igneous rocks.

INTRUSIVE IGNEOUS ROCKS
		GRANITE - light-colored intrusive rock (has large crystals since it cooled slowly well below the Earth's surface), with abundant feldspar and some quartz; rock of this composition makes up the bulk of the continental crust
		GABBRO - dark-colored intrusive rock (has large crystals since it cooled slowly well below the Earth's surface), commonly rich in pyroxene minerals (dark); the deeper portion of oceanic lithosphere
EXTRUSIVE IGNEOUS ROCKS
		BASALT - dark-colored extrusive rock (has small crystals since it cooled quickly at or near the Earth's surface), with abundant feldspar and dark minerals (amphiboles and pyroxenes); typical oceanic crust and the kind of rock that forms from the lavas erupted by volcanoes in Hawaii and Iceland.
		ANDESITE - intermediate-colored extrusive rock (has primarily small crystals since it cooled quickly at or near the Earth's surface); typical volcanic rock of subduction zones (e.g. Andes, Cascades) where magmas are produced by partial melting of both oceanic and continental crust.

Sedimentary Rocks

Metamorphic Rocks

Common Rocks

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