A rock is any naturally occurring solid mass of mineral matter. It may be solidified molten magma or sediments, but it most commonly consists of minerals.
Rock may be hard or soft and in varied colours. For example, granite is hard, soapstone is soft. Petrology is the science of rocks.
Rocks are usually grouped into three main groups: igneous rocks, sedimentary rocks and metamorphic rocks. Igneous rocks are formed when magma cools in the Earth’s crust, or lava cools on the ground surface or the seabed.
Sedimentary rocks are formed by diagenesis or lithification of sediments, which in turn are formed by the weathering, transport, and deposition of existing rocks.
Metamorphic rocks are formed when existing rocks are subjected to such high pressures and temperatures that they are transformed—something that occurs, for example, when continental plates collide.
There are many different kinds of rocks that are grouped under three families on the basis of their mode of formation.
They are:
- Igneous Rocks —solidified from magma and lava;
- Sedimentary Rocks — the result of deposition of fragments of rocks by exogenous processes;
- Metamorphic Rocks — formed out of existing rocks undergoing recrystallisation.
