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migmatite


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A coarse-grained, heterogeneous mixed rock consisting of: (a) a high-grade metamorphic component with a gneissose texture (see metamorphic grade); and (b) an igneous component with a granite mineralogy and a foliated or unfoliated texture (see foliation). Migmatites are found in high-grade metamorphic terrains where a sequence from high-grade metamorphic rocks through migmatites to granite bodies is often seen in the field. The granite component is thought to form by partial melting of the rock during extreme metamorphism. Migmatites may thus be a record of the initial stages in the generation of large bodies of granite magma and, as such, they would represent the high-temperature boundary between metamorphic and igneous rocks. Migmatites have an attractive appearance, often being marked with irregular small stripes or patches of contrasting shades ranging from almost white to dark grey, and are widely used as building stone, sometimes being polished for ornament.

(a) a high-grade metamorphic component with a gneissose texture (see metamorphic grade); and (b) an igneous component with a granite mineralogy and a foliated or unfoliated texture (see foliation).

Subjects: Earth Sciences and Geography.


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