Here's a breakdown:

Igneous Rocks:

* Formed from the cooling and solidification of magma (molten rock) or lava.

* Examples: Granite, basalt, gabbro

Sedimentary Rocks:

* Formed from the accumulation and cementation of sediments like sand, mud, or organic matter.

* Examples: Sandstone, limestone, shale

Metamorphic Rocks:

* Formed when existing rocks are transformed by heat, pressure, or chemical reactions.

* Examples: Marble, slate, gneiss

The composition of the crust varies depending on whether it's continental crust or oceanic crust:

Continental Crust:

* Thicker and less dense than oceanic crust.

* Primarily composed of granite and other felsic rocks rich in silica, aluminum, sodium, and potassium.

Oceanic Crust:

* Thinner and denser than continental crust.

* Mostly made of basalt and gabbro, which are mafic rocks rich in magnesium and iron.

In addition to the major rock types, the crust also contains a small percentage of other materials, including:

* Minerals: Quartz, feldspar, mica, etc.

* Water: Found in various forms, including groundwater and ice.

* Organic matter: Decaying plant and animal material.

It's important to note that the Earth's crust is constantly changing as a result of plate tectonics, erosion, and other geological processes.