The major types of rocks are igneous rocks, sedimentary rocks and metamorphic rocks. let’s know more about these types of rocks in ensuing paragraphs.
The hot lava that flows out of a volcanic eruption cools down, solidifies over a period of time and forms igneous rocks. The word igneous is derived from the Latin word ignis- which means ‘fire’. Igneous rocks are also called primary rocks.
- Basalt is an example.
Over a period of several years, sediments carried by agents of gradation like water, ice, wind and the sea are deposited in layers over the earth. The sediments may consist of weathered and fragmented rock materials, micro-organisms and plant and animal remains.
As the deposition of sediments builds up, the pressure exerted by the upper layers squeezes the sediment into layered rocks called sedimentary rocks.
- Shale, sandstone and conglomerate are some examples of sedimentary rocks.
Under conditions of intense heat and pressure existing rocks metamorphose or change completely into new kinds of rocks. Such rocks are called metamorphic rocks. The word metamorphic is derived from the Greek word meta- which means ‘change’ and morphe- which means ‘form’.
Some examples of metamorphic rocks are:
- Clay changing into slate
- Limestone changing into marble
- Coal changing into diamond