Metamorphic rocks form under high pressure and temperature conditions, altering the mineral composition without full melting.
Metamorphic rocks are formed when sedimentary or igneous rocks are subjected to high temperature and pressure, causing changes in their mineral composition. In the given scenario, the sedimentary rock that fell into the ocean and later turned into a metamorphic rock did not become an igneous rock because it did not experience high enough temperatures to melt, which is necessary for the formation of igneous rocks like granite or basalt. The process of metamorphism altered the rock's structure without melting it completely.
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