Migmatite

Migmatite is a rock in the frontier between igneous and metamorphic rocks. They form on extreme temperature-pressure conditions, where partial melting occurs in pre-existing rocks. On one hand migmatites are not crystallized from a totally molten material, on the other are not the result of solid state reactions as metamorphic rocks. Migmatites are composed of a neossome, new material crystallized from incipient melting, and a paleossome, old material that resisted melting. Commonly, migmatites are extremely deformed rocks that represent the base of eroded, old mountain chains.

See also: igneous rocks, metamorphic rocks, list of rocks