Have you have heard that caterpillars metamorphose into butterflies? Well, rocks can metamorphose too! They don't grow wings like a butterfly. But they do change! Rocks metamorphose when they are in a place that is very hot and pressure is high. You can find such a place where Earth's tectonic plates are coming together. There, the colliding plates squish rocks, and hot pools of magma heat them deep underground.
Some rocks only change a little, while others change a lot. When a rock is metamorphosed, its mineral crystals change. Usually, the same chemical ingredients are used to form new crystals during metamorphism. Sometimes new types of minerals grow that weren't in the rock before.
Often, flat minerals like mica become lined up perpendicular (at a right angle) to the direction of pressure. When minerals within a metamorphic rock are organized this way, it is called foliation. Some metamorphic rocks are foliated and others are non-foliated.
Any type of rock, can be metamorphosed. The rocks are changed either in small areas of contact metamorphism or large areas of regional metamorphism.

你听说过毛毛虫变化成蝴蝶吗？好吧，石头其实也会变化哦！他们不会像蝴蝶一
样长出翅膀。但他们确实会改变！岩石处在一个非常热并且有高压的地方就会发
生变化。你可以在地球构造板块接触的地方找到这样的地点。在那里，碰撞的板
块会挤扁岩石，高温的岩浆池塘在深深的地底加热岩石。
有些岩石只发生了一点点改变，而其他的改变了很多。当一个岩石发生变质以后
，它的矿物晶体发生变化。一般来说，同样的化学作用在变质时同时产生了新晶
体。有时候在岩石中会出现以前没有出现过的新种类矿物。
通常，扁平状的矿物，像是云母，会顺着压力的方向垂直排列（从正确角度来看
）。当变质岩中的矿物如此排列时，它就被称作“叶理”。有些变质岩有叶理，
另一些则没有。
任何种类的岩石都可以发生变质。岩石可以在小范围内发生接触变质或在大范围
内发生区域变质。