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X-ray crystallographic data are of particular importance to the mineralogist. Beyond the considerations of structural chemistry they provide. one of the most accurate methods for phase and/or compositional determination and for obtaining _the molar volumes and densities of minerals {Robie and Bethke, 1962).
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Land-pebble phosphate, hard-rock phosphate, and river-pebble phosphate are the three types of phosphatic rock found in Florida. This report is concerned primarily with the land-pebble deposits, the only type which contains a significant amount of uranium. The most productive part of the land-pebble district is in Polk and Hillsborough Counties, in the west-central part of the Florida peninsula. Phosphate occurs in both the Hawthorn formation of lower middle Miocene age and the Bone Valley formation of Pliocene age. The phosphate in the Bone Valley is generally of higher grade, probably as the result of mechanical reworking and further precipitation during submergence in Pliocene time. In a few places, leached parts of the Hawthorn formation are also of minable grade. , Pleistocene terrace deposits and beach sands unconformably overlie the Bone Valley. In Polk and Hillsborough Counties, the high-grade part of the land-pebble phosphate district, uranium occurs principally in the Bone Valley formation and is concentrated in the upper part of the formation, which has been leached by ground water. The maximum tenor found to date is 0.1 percent uranium. The basal member of the Bone Valley has a maximum grade of .02 percent uranium, and averages about .01 percent uranium. Fresh, unweathered Hawthorn formation has little or no uranium, but leached Hawthorn, rich in P 2 O 5 , contains a maximum of 0.01 percent uranium. The Pleistocene sands have no uranium except where they contain reworked phosphatic material from the Bone Valley formation. South of the high- grade district, in Manatee and Hardee Counties, the Bone Valley, Hawthorn, and Pleistocene formations contain only very minor amounts of uranium. The uranium in the land-pebble deposits was probably syngenetic in origin. Subsequent leaching of soluble material has resulted in residual enrichment of uranium. The uranium seems to be associated with the phosphate mineral.
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