- Phosphorite
A phosphorite or phosphate rock is a non-detrital
sedimentary rock which contains high amounts ofphosphate bearing minerals. The phosphate content of phosphorite is at least 20% which is a large enrichment over the typical sedimentary rock content of less than 0.2%.Blatt, Harvey and Robert J. Tracy, "Petrology", Freeman, 1996, 2nd ed. pp. 345-349 ISBN 0-7167-2438-3 ] The phosphate is present asfluorapatite typically incryptocrystalline masses (grain sizes < 1 μm) referred to ascollophane . The dark brown to black beds range from a few centimetres to several metres in thickness. The layers contain the same textures and structures as fine grainedlimestone s and may represent diagenetic replacements ofcarbonate minerals by phosphates.Phosphorites are known from
Proterozoic banded iron formation s inAustralia , but are more common fromPaleozoic andCenozoic sediments. ThePermian Phosphoria Formation of the western United States represents some 15 million years of sedimentation reaches a thickness of 420 metres and covers an area of 350 000 km2. Commercially mined phosporites occur in France, Belgium, Spain, Morocco, Tunisia and Algeria. In the United States phosphorites have been mined in Florida, Tennessee, Wyoming and Idaho. [Klein, Cornelis and Cornelius S. Hurlbut, Jr., "Manual of Mineralogy", Wiley, 1985, 20th ed., p. 360, ISBN 0-471-80580-7 ]References
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