An estimated 1,100 million metric tons of high-grade bauxite (50% Al 2 O 3 and 5% or less SiO 2 ) is present on the island of Jamaica. The bauxite overlies limestone of middle Eocene to lower Miocene age and accumulates in karst depressions and fault-controlled valleys.The principal parent material of bauxite is Miocene volcanic ash. Significant thicknesses of bentonitic limestone and bentonitic clay have been found in the middle and upper Miocene carbonate section along the north coast of Jamaica. It is believed that volcanic ash alters to bauxite by desilication of glass, plagioclase, biotite, and ferromagnesians through either phyllosilicate intermediate phases or gel and imogolite. The insoluble residue of middle Eocene to lower Miocene host rocks and alluvium from Cretaceous and lower Tertiary aluminous rocks contribute very little to bauxite deposits and associated soils.The most important control on the genesis and distribution of bauxite in Jamaica is subsurface drainage. Vertical drainage of vadose water through the faulted host limestone karst is extremely efficient in leaching silicon from the overlying soils and concentrating aluminum in the form of bauxite.