Question

How are metamorphic rocks classified?

Answer 1

Hint: Generally speaking, naturally-occurring solid masses made up of minerals and mineraloid matter are known as rocks. They are found largely in the earth’s crust and a relatively smaller fraction in the upper mantle of the earth. The three main categories of rocks are igneous, sedimentary and metamorphic based on their process of formation. Metamorphic rocks, as the name implies, are formed as a result of metamorphism which leads to changes in the minerals and geological texture of pre-existing rocks from heat and pressure.

Complete answer: Metamorphic rocks can be categorised into— foliated and nonfoliated metamorphic rocks, both of which are derived from either igneous or sedimentary rocks, however, the process of recrystallisation makes them distinct. Foliated rock is formed due to unequal pressure applied during recrystallisation while a non-foliated rock is formed due to equal pressure applied during the same. Foliated rocks are made up of finer particles and may break or separate into thin layers. Conversely, non-foliated rocks have a granular appearance because they contain coarse grains. Examples of foliated rocks are slate, phyllite, schist, gneiss, etc and examples of non-foliated rocks are marble, quartzite, hornfels, anthracite coal, etc.

Note: Igneous rocks are made up of solidified lava and volcanic material which may either seep through pre-existing rocks and crystallise or erupt during volcanic activity and cool down over time to form rocks. Sedimentary rocks are formed due to the deposition of minerals and organic matter in layers on top of each other over a long period.