What are rocks? Name the main types of rocks with two examples of each.

Rocks are aggregates of one or more minerals, without having a definite chemical composition. The rocks may be composed of hard materials like granite and marble or soft like chalk, clay and sand.

The main types of rocks are:

1. Igneous rocks or Primary rocks:
   1. Intrusive igneous rocks — For example, granite and dolerite
   2. Extrusive igneous rocks — For example, basalt, pumice
2. Sedimentary rocks — For example, sandstone and limestone
3. Metamorphic rocks — For example, marble and quartzite