Aluminium is quite reactive and hence does not occur in nativie forms. Aluminium is the third most abundnat element in the earth's crust. The important ores of aluminium are i) Bauxite Al_(2)O_(3)2H_(2)O ii) Cryolite Na_(3)AlF_(6) iii) Feldspar KAISi_(3)O_(8) iv) Alunite K_(2)SO_(4)Al_(2)(SO)_(4)Al(OH)_(3) Aluminium is extracted from Bauxite. Bauxite is generally associated with iron oxide and silica as impurity. Bauxite ore containing excess of ferric oxide (Red bauxite) is powdered and digested with a strong solution of caustic soda in an auto clave when alumina (Al_(2)O_(3) passes into solution as sodium aluminate while ferric oxide remains undissolved and is filtered out- Al_(2)O_(3) + 2Na to 2NaAlO_(2) + H_(2)O The solutioin is diluted with water and a small amount of freshly precipated aluminium hydroxidel is added as seeding agent. The precipated Al(OH)_(3) is filtered, washed and ignited to get pure alumina. 2Al(OH)_(3) overset(Delta)to underset("Alumina") Al_(2)O_(3) + 3H_(2)O Pure alumina is dissolved in molten cryolite and is electrolyted using graphite electrodes. Aluminium obtained after this step is 99% pure. It can further be refined by Hoope's process. Principle ore of aluminium is