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

2. Sedimentary rocks: These rocks are formed from the accumulation and cementation of sediments, which are fragments of other rocks, minerals, or organic matter. Examples include sandstone, limestone, and shale.

3. Metamorphic rocks: These rocks are formed when existing igneous or sedimentary rocks are subjected to intense heat and pressure. Examples include marble, slate, and gneiss.