1. Igneous rocks: Formed from the cooling and solidification of magma (molten rock) or lava. Examples include granite, basalt, and obsidian.
2. Sedimentary rocks: Formed from the accumulation and cementation of sediments, such as sand, mud, and organic remains. Examples include sandstone, limestone, and shale.
3. Metamorphic rocks: Formed from existing rocks (igneous, sedimentary, or other metamorphic rocks) that have been transformed by heat and pressure. Examples include marble, slate, and gneiss.