Types of Rocks

Igneous Rocks:

• Igneous rocks are crystalline solids which form directly from the cooling of magma.
• This is an exothermic process (it loses heat) and involves a phase change from the liquid(magma) to the solid state.
• The earth is made of igneous rock - at least at the surface where our planet is exposed to the coldness of space.
• Igneous rocks are given names based upon two things: composition (what they are made of) and texture (how big the crystals are).
• These rocks are harder and granular.
• There is no layer of igneous rocks and fossils are not found in igneous rocks.
• Rocks formed by the cooling of the molten matter beneath the earth surface are called intrusive igneous rocks and are crystalline rocks.
• Sometimes the molten mater comes out on the earth surface and forming extrusive igneous rocks e.g. Obsidian, basalt.

Sedimentary rocks:

• They are formed by deposition and sedimentation of sediments over a long period.
• Sedimentary rocks are called secondary because they are often the result of the accumulation of small pieces broken off of pre-existing rocks.
• Sandstone, limestone, shale are some example of sedimentary rocks.

Metamorphic rocks:

The metamorphic get their name from "meta" (change) and "morph" (form).

The nature of igneous and sedimentary rocks changes due the effects of tremendous heat or pressure and the newly transformed rocks are called metamorphic rocks.