Here's a breakdown:

* Igneous Rocks: These rocks are formed from the cooling and solidification of magma (molten rock beneath the surface) or lava (molten rock erupted onto the surface). Examples include granite, basalt, and obsidian.

* 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.

* Metamorphic Rocks: These rocks are formed when existing rocks are transformed by heat, pressure, or chemical reactions. Examples include marble (from limestone), slate (from shale), and gneiss (from granite).

Composition of the crust:

* Oxygen (O): The most abundant element, making up about 46.6% of the crust by weight.

* Silicon (Si): The second most abundant element, making up about 27.7% of the crust by weight.

* Aluminum (Al): The third most abundant element, making up about 8.1% of the crust by weight.

* Iron (Fe): The fourth most abundant element, making up about 5.0% of the crust by weight.

* Calcium (Ca): The fifth most abundant element, making up about 3.6% of the crust by weight.

Two types of crust:

* Continental crust: Thicker (average 35 km) and less dense, primarily composed of granite and other felsic rocks.

* Oceanic crust: Thinner (average 7 km) and denser, primarily composed of basalt and other mafic rocks.

It's important to note that the Earth's crust is constantly being recycled through the process of plate tectonics. New crust is formed at mid-ocean ridges, and old crust is destroyed at subduction zones.