What do you mean by rocks? Name the three major classes of rocks.

Explanation

The earth.s crust is composed of rocks. A rock is made up by aggregate of one or more minerals. Rock may be hard or soft and in varied colours. For example, granite is hard, soapstone is soft. Gabbro is black and quartzite can be milky white. Rocks do not have definite composition of mineral constituents. Feldspar and quartz are the most common minerals found in rocks.
There are many different kinds of rocks which are grouped under three families on the basis of their mode of formation. They are: (a) Igneous Rocks (b) Sedimentary Rocks and (c) Metamorphic Rocks.