Jos, Kaduna, Nigeria
Sapphire-bearing placer deposit near Jos in the southeastern part of Kaduna state.Sapphires in association with hematite, goethite, and gibbsite are extracted from the upper horizon of alluvial deposits, 0.5 to 1 m from the surface. Sapphire crystals have barrel-like, tabular or prismatic shapes and are partly rounded. The colour is mostly blue and less often yellow. Refractive index is 1.759 - 1.771. Solid inclusions in sapphires include zircon, albite and uranpyrochlore.
Because of their dark colour, the blue sapphires from Kaduna are mainly cut into cabochons.
Ref: E.Ya. Kievlenko (2003) Geology of gems, p. 68