- © The Mineralogical Society Of America
The phosphorous cycle filters through both the biological and geological worlds, and sedimentary phosphates exist at the interface between these two portions of the global phosphorous cycle. Sedimentary phosphates form only when the proper physical conditions and biological activity coincide. Once deposited, the phosphate (PO43−) crystallizes into the mineral carbonate-fluorapatite (CFA). This mineral, with substitution of CO32− for PO43−, compositionally falls between the familiar forms of fluorapatite found in igneous and metamorphic rocks and the apatites found in biological material, including our own bones and teeth. Finally, through mining and processing, it is these sedimentary phosphates that are used as fertilizers and additives for food production and other activities and are subsequently returned to the biosphere.
The unique settings in which phosphorites form, those areas where phosphate is concentrated millions of times above normal and sedimentation rates are drastically slowed, are not fully understood, and have been the subject of sometimes intense scientific debate over the last century and a half. Furthermore, the mineralogy of these deposits is unique, difficult to study, and contentious. Because of our dependence on phosphate for use in fertilizers and other agricultural and chemical uses, these deposits are interesting not only from a scientific viewpoint but from an economic standpoint as well. However, like many mining operations, phosphate mining has environmental problems that must be addressed.
This chapter provides an overview of the salient points in phosphorite formation, mineralogy, and mining and puts into context the current work being undertaken on the Phosphoria Formation in southeastern Idaho. This chapter does not provide a full description of all the sedimentalogical, mineralogical, and industrial work that has been done on sedimentary phosphates; indeed numerous full volumes have been published on phosphorites and more will undoubtedly follow.
For large-scale phosphorites to …