A metamorphic rock is made from igneous rocks, sedimentary rocks, or other metamorphic rock. It is made by either compaction or cementation. Compaction is when layers of sediments pile over a rock and then squeeze together. Cementation is when the rock is held together by the sediments. Metamorphic rocks can be either foliated or non-foliated. Foliated rocks have layers, while non-foliated rocks don't. A rock that has been changed into a metamorphic rock is also called the parent rock. Similarly, a metamorphic rock can change back into a sedimentary rock by the opposite process.
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