Bauxite is a brown to reddish-brown sedimentary rock that is the primary source of aluminum. It is composed primarily of the minerals gibbsite, boehmite, and diaspore, and is formed from the weathering of aluminum-rich rocks such as granite and syenite. The colour of bauxite varies from light brown to reddish-brown, and can also be gray or white in some cases. The variation in colour is primarily due to the different mineral compositions and the degree of weathering of the bauxite.