The Bayer process is the principal industrial means of refining bauxite to produce  alumina (aluminium oxide) and was developed by Carl Josef Bayer. Bauxite, the most important ore of aluminium, contains only 30–60% aluminium oxide (AlO), the rest being a mixture of silica, various iron oxides, and titanium dioxide. The aluminium oxide must be further purified before it can be refined into aluminium.
The Bayer process is also the main source of gallium as a byproduct despite low extraction yields.