The titanium mineralogy of bauxites, associated clays and parent rocks from Arkansas, France, Jamaica, Oregon, Ireland and Surinam has been investigated. The most abundant titanium oxide in the parent rocks is ilmenite. Very small amounts of leucoxene, rutile, anatase and titaniferous hematite are also present. These same minerals plus titaniferous magnetite and menaccanite occur in the clays and bauxites but in different relative percentages. Leucoxene, an alteration product of ilmenite, is a major constituent of the + 325 mesh heavy mineral fractions of bauxites and associated clays. X-ray studies show that leucoxene in these materials consists of rutile and anatase. The alteration of primary ilmenite to secondary oxides follows three different routes. In general, the nature of the parent rock appears to exert little if any influence on the formation of the TiO 2 polymorphs from ilmenite or on the alteration products of ilmenite, although the modes of alteration are more varied in Arkansas bauxite than in bauxite from the other localities. The bulk of the TiO 2 in bauxites and associated clays is in the -- 325 mesh fraction. This finely divided TiO 2 comes in part from the titanium released during the alteration of sphene and other titanium-bearing silicates of the parent rocks and in part from the alteration of ilmenite.