1. Igneous rocks: Formed from the cooling and solidification of magma (molten rock) or lava. Examples: granite, basalt, obsidian.

2. Sedimentary rocks: Formed from the accumulation and cementation of sediments, such as sand, mud, or shells. Examples: sandstone, limestone, shale.

3. Metamorphic rocks: Formed when existing igneous or sedimentary rocks are transformed by heat, pressure, or chemical reactions. Examples: marble, slate, gneiss.