It is largely made up of the minerals Gibbsite Al ( OH ) 3 , Boehmite Î - AlO ( OH ) , and Diaspore Î - AlO ( OH ) , together with the iron oxides Goethite and Hematite , the clay mineral Kaolinite and small amounts of Anatase TiO2 . This form of rock consists mostly of the minerals gibbsite Al ( OH ) 3 , boehmite Î - AlO ( OH ) , and diaspore Î - AlO ( OH ) , in a mixture with the two iron oxides goethite and hematite , the clay mineral kaolinite , and small amounts of anatase TiO2 .