Introducing Metamorphism / Введение в метаморфические процессы

Metamorphism (from the Greek words meta = change and morphos = form) is a geological process that changes pre-existing igneous and sedimentary rocks into new rocks – metamorphic rocks – that look quite different from the rocks they started out as. Metamorphism can even change pre-existing metamorphic rocks into new, and different looking, metamorphic rocks. When rocks are changed like this they are said to become metamorphosed, but one should note that the related word metamorphosis has no place in geology. It applies to other kinds of change, such as from a tadpole to a frog, and is not a synonym for metamorphism.
Metamorphism takes place underground, usually deep underground at a high temperature. Since it cannot be watched as it happens, it is often portrayed as being more difficult to grasp than the formation of igneous or sedimentary rocks. Igneous rocks can be seen being made when, for example, volcanic lava cools and hardens. The formation of sedimentary rocks can be watched as grains of sand, for example, are moved by rivers and deposited on the seabed. Yet the very fact that metamorphic rocks originate ‘out of sight’ makes them all the more intriguing. The detective work involved in figuring out how they were made can be both challenging and rewarding. <...>