Types of Rocks (Information and Facts)

 Rock 

The solids parts of the Earth's crust are called rocks. Most of the rocks are made up of two or more minerals.
The sientific study of rocks is called petrology. On the basis of the mode of origin, rocks are of three types.

1. Igneous Rocks

• It is also called primary rocks as they are formed due to the cooling, solidification and crystallisation of hot and molten magma e.g. Granite. When granite rocks get metamorphased, they form gneiss.
• There are no layers in igneous rocks.
• Fossils are not found in igneous rocks.
• Igneous rocks are generally harder and granular.

2. Sedimentary Rocks

• These rocks are formed by the deposition, sedimentation and lithification of sedimentations over a long period of time.
• As layers over layers get deposited, over a period of time, unified sedimentary rocks are formed on account of the tremendous pressure exerted by the layers above. 
• Sometimes the remains of plants. dead animals etc are found in the deposited material.
• Sandstone, limestone and shale are some examples of sedimentary rocks.

3. Metamorphic Rocks

• The nature of igneous and sediimentary rocks changes due to the effect of tremendous heat or pressure and new, transformed rocks called metamorphic rocks are formed.
• Marble and slate are example of metamorphic rocks. 
• Minerals in the rocks get restructured on due to heat and pressure. This brings a change in the original form of the rocks.

Metamorphic