Deltaic deposits of pachnolite and fluorite occur in Tampa Bay, Florida, as a result of chemical precipitation from a fluoride-rich effluent from a phosphate chemical plant. The deposits are crusts up to 8 cm in thickness and cover a total of 5 ha. Crusts range from discontinuous masses to a solid shield with superimposed distributaries. These deposits are the only known deposits where pachnolite and fluorite can be shown to have formed in a marine sedimentary environment.--Journal abstract.