A gibbsite-containing quartz sandstone occurs near Fort Walton, Florida. Scanning electron micrographs show the gibbsite of the matrix to be anhedral which is the typical morphology in many deposits of bauxite. At the contact surface with the quartz grains, however, the gibbsite crystals are euhedral, as if recrystallized from solution. No kaolinite was detected at this interface despite both Al 2 O 3 and SiO 2 being available for combination at the contact. Alternative hypotheses of origin are a) deposition of gibbsite in a sandstone from solutions that obtained the alumina by leaching from a gibbsite zone above, and b) development of gibbsite by intense leaching of clastic sediments on a Tertiary terrace, during which fine quartz sand, probably aeolian, was added.

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