|Abstract from DBPedia||
Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock (protolith) is subjected to heat (temperatures greater than 150 to 200 °C) and pressure (1500 bars), causing profound physical and/or chemical change. The protolith may be a sedimentary rock, an igneous rock or another older metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and are classified by texture and by chemical and mineral assemblage (metamorphic facies). They may be formed simply by being deep beneath the Earth's surface, subjected to high temperatures and the great pressure of the rock layers above it. They can form from tectonic processes such as continental collisions, which cause horizontal pressure, friction and distortion. They are also formed when rock is heated up by the intrusion of hot molten rock called magma from the Earth's interior. The study of metamorphic rocks (now exposed at the Earth's surface following erosion and uplift) provides information about the temperatures and pressures that occur at great depths within the Earth's crust.Some examples of metamorphic rocks are gneiss, slate, marble, schist, and quartzite.
変成岩（へんせいがん、英: metamorphic rock）とは、既存の岩石が変成作用を受けた岩石のこと。変成岩の原岩は火成岩、堆積岩など種類は問わず、変成岩がさらに変成作用を受ける場合もある。 変成岩は、原岩になった岩石の種類と、受けた変成作用の性質により分類される。変成作用の主な要因は熱と圧力で、変成作用の種類により温度と圧力の条件が異なる。 1950年代ごろまでは、旧字体の變の字を使い、變成岩と書かれていた。