Migmatite
U.S. Geological Survey photo (fair use policy)
Migmatite has been buried deep and squeezed hard. Migmatite is the same material as gneiss, but it has been brought to melting or near-melting so that the veins and layers of minerals became warped. In many cases the darker rock 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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