General Knowledge - Rocks


  • Rock is the solid mineral material that forms part of the surface of the earth, exposed on the Earth’s surface or underlying the soil.

  • Rock is divided into following three types −

    • Igneous Rocks

    • Sedimentary Rock

    • Metamorphic Rock

Igneous Rock

  • Igneous Rock is normally formed by the solidification of the molten magma.

  • All other types of rocks are formed by the igneous rock; therefore, igneous rock is also known as primary rock.

  • About 95% of the Earth’s crust is made of igneous rock.

  • Granite, Basalt, and Volcanic rock are the major types of igneous rock.

Igneous Rocks

Sedimentary Rock

  • The rocks, which is formed because of the deposition of weathered remains of igneous rocks, is known as ‘Sedimentary Rock.’

  • Sedimentary rocks share 5% of the Earth’s surface, but cover (in terms of area) about 75% of Earth’s (exposed) surface.

  • Sedimentary rocks also contain organic materials (i.e. source of energy for the human beings).

  • Major examples of sedimentary rocks are Gypsum, Limestone, Chalk, Coal, Conglomerates, Sandstone, Claystone, etc.

Sedimentary Rocks

Metamorphic Rock

  • Because of the intense pressure, high fluctuating temperature, and presence and absence of moisture and chemicals, over a period of time, igneous rock or sedimentary rocks get modified (metamorphosed) and called as ‘Metamorphic Rock.’

  • Major examples of metamorphic rock are Slate, Gneiss, Marble, Quartzite, etc.

Metamorphic Rocks