The three main types of rocks that make up the Earth's crust are:

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 (fragments of other rocks, minerals, or organic matter). Examples include sandstone, limestone, and shale.

3. Metamorphic Rocks: Formed when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are transformed by heat, pressure, or chemical reactions. Examples include marble, slate, and gneiss.