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plural migmatites
(geology) Any rock of mixed appearance, being an intimate mixture of granite and older rock, specifically from intense metamorphism which partially melts the rock, causing it to recrystallize in a state intermediate between igneous and metamorphic. quotations
More specifically, many of these rocks are described as migmatites, in which the pink veins seem to blend insensibly into a kind of swirling granite.
2004, Richard Fortey, The Earth, Folio Society, published 2011, page 163