Igneous rock

Igneous rock, one of the 3 main classes of rocks, that whose origin is the solidification of molten material, or detrital volcanic material. It crystallizes from lava at the earth's surface (extrusion) or from magma beneath (intrusion). There are 2 main classes: Volcanic rocks are extruded, typical examples being lava and pyroclastic rocks. Plutonic rocks are intruded into the rocks of the earth's crust at depth, a typical example being granite; those forming near to the surface are sometimes called hypabyssal rocks. Types of intrusions include batholiths, dikes, sills, and laccoliths. As plutonic rocks cool more slowly than volcanic, they have a coarser texture, more time being allowed for crystal formation.

See also: Basalt; Granite.