Aluminum oxide grit is sourced from bauxite ore. This ore is the primary source of aluminum metal. Bauxite contains primarily aluminum oxides as well as other oxides and impurities.
Standard Aluminum Oxide Grit is a refined (see Bayer Process) material to a purity of about 95% alumina (Al2O3). The brown/gray color is due to minor, natural impurities in the material.
White Aluminum Oxide is >99% pure aluminum oxide. This is obtained by converting the bauxite ore to aluminum metal (see Hall-Heroult Process). The aluminum metal is then reacted with oxygen to create a white crystalline alumina.