Types of Rocks

🔹 Sedimentary Rocks

➨ Sedimentary rocks are formed by the deposition of organic and non-organic matter over a period of time.

➨ Sedimentary rocks hold all reserves of coal, oil and natural gas.

➨ Sedimentary rocks often contain fossils.

➨ About 75 percent surface area of the earth is covered by the sedimentary rocks.

➖Example: Lignite, Coal, Sandstone, Shale.

🔹 Igneous rocks

➨ Igneous rocks forms through the cooling and solidification of magma (molten rock deep inside the earth) or lava.

➨ Igneous rocks made up 85 percent or more of the earth's crust.

➨ Igneous rocks are divided into two main categories: 

  ➖Plutonic rock : Example - Granite

  ➖Volcanic rock : Example - Basalt

🔹 Metamorphic Rocks

➨ Due to unfavourable condition of pressure and change in temperature under the earth’s surface Igneous and Sedimentary rocks undergo change. This change leads to the formation of Metamorphic Rocks.

➨ Metamorphic rocks may be classified as foliated or non-foliated.

➨ Metamorphic rocks are divided into two main categories: 

  ➖Foliated metamorphic rocks : Example - Mica

  ➖Non-foliated metamorphic rock : Example - Marble and Quartzite