1. Igneous Rocks:

* Formation: Igneous rocks are formed from the cooling and solidification of magma (molten rock) or lava (magma that has erupted onto the Earth's surface).

* Intrusive Igneous Rocks: When magma cools and solidifies slowly beneath the Earth's surface, it forms large crystals, resulting in intrusive igneous rocks like granite.

* Extrusive Igneous Rocks: When lava cools and solidifies quickly on the Earth's surface, it forms smaller crystals, resulting in extrusive igneous rocks like basalt.

2. Sedimentary Rocks:

* Formation: Sedimentary rocks are formed from the accumulation and cementation of sediments, which are fragments of other rocks, minerals, or organic matter.

* Clastic Sedimentary Rocks: These rocks are formed from fragments of other rocks, such as sandstone, shale, and conglomerate.

* Chemical Sedimentary Rocks: These rocks are formed from the precipitation of minerals from water, such as limestone, rock salt, and gypsum.

* Organic Sedimentary Rocks: These rocks are formed from the accumulation of organic matter, such as coal and oil shale.

3. Metamorphic Rocks:

* Formation: Metamorphic rocks are formed when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are transformed by heat, pressure, or chemical reactions.

* Contact Metamorphism: This occurs when rocks are heated by nearby magma or lava.

* Regional Metamorphism: This occurs over large areas due to tectonic plate collisions and the immense pressure and heat associated with it.

Key Differences:

* Igneous rocks: Formed directly from molten rock.

* Sedimentary rocks: Formed from fragments of other rocks or organic matter.

* Metamorphic rocks: Formed from the transformation of existing rocks by heat, pressure, or chemical reactions.