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Migmatite

Pictures of Metamorphic Rock Types

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Migmatite is the same material as gneiss, but brought close to melting by regional metamorphism so that the veins and layers of minerals became warped and mixed. (more below)
Half-melted gneiss
Photo (c) 2008 Andrew Alden, licensed to About.com (fair use policy)
Migmatite has been buried very deep and squeezed very hard. In many cases the darker part of the rock, consisting of biotite mica and hornblende, has been intruded by veins of lighter rock consisting of quartz and feldspar. With its curling light and dark veins, migmatite can be very picturesque. Yet even with this extreme degree of metamorphism, the minerals are arranged in layers and the rock is clearly classified as metamorphic.

If mixing is even stronger than this, a migmatite can be hard to distinguish from the igneous rock granite. Because it isn't clear that true melting is involved, even at this degree of metamorphism, geologists use the word anatexis (loss of texture) instead.

For more photos see the Metamorphic Rocks Gallery.

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