The type locality of bauxite is Les Baux, Provence, France. Discovered by P. Berthier in 1821, the red claylike specimen from the type locality is almost free of silica and contains 52 percent alumina. Arkansas bauxite differs slightly from the French type specimen. The principal ore mineral in Arkansas bauxite is gibbsite, the trihydrate of alumina, rather than the dihydrate of aluminum in the original type specimen. Free silica, silt, iron hydroxides, and clay minerals are also associated with Arkansas bauxite.
Color ranges from light gray to tan, brown and red.
Color is not indicative of ore grade or of iron content. For example, brick red bauxite might contain little iron. Above conditions persist a long time. The Arkansas bauxite region covers about 275 square miles near the center of the state in Pulaski and Saline Counties. Bauxite ore clusters on and around masses of nepheline syenite, a porous, aluminum-rich, igneous rock.