Igneous rock results from volcanic activity such as lava, or crystalization from magma and other conditions of intense heat acting on the surrounding mantle and crust.

Igneous rock comprises one of three origins of parent material for soils.

Igneous rocks form when molten magma pushes up into the crust or through it. Igneous rock contains various minerals in seemingly randomly arranged, interlocking crystals. There are two types of igneous rock - intrusive and extrusive.

Intrusive rocks cool slowly with big crystals. They cool slowly because they're underground. An example of an intrusive rock is granite. Granite is very hard.

Extrusive rocks cool quickly with small crystals. An example of an extrusive igneous rock is basalt.

Ig"ne*ous (?), a. [L. igneus, fr. ignis fire; allied to Skr. agni, Lith. ugnis, OSlav. ogne.]

1.

Pertaining to, having the nature of, fire; containing fire; resembling fire; as, an igneous appearance.

2. Geol.

Resulting from, or produced by, the action of fire; as, lavas and basalt are igneous rocks.

 

© Webster 1913.