Phosphorite
Phosphorite, also known as phosphate rock, is a sedimentary rock that contains at least 50% phosphate minerals, primarily in the form of fluorapatite. It is characterized by its high concentration of phosphorus, making it significantly richer in this element compared to typical sedimentary rocks. Found in various environments, phosphorite deposits can accumulate on seabed floors, particularly around large landmasses, and at fossil sites like bone beds where skeletal remains contribute to phosphate concentrations. The formation of phosphorite involves processes such as phosphatization, where phosphate-rich liquids infuse sediment.
Phosphorites are categorized into three groups based on sediment accumulation and erosion, including pristine, condensed, and allochthonous types. The phosphorus in these rocks is supplied through rivers, ocean upwelling, and other natural processes, and is vital for plant growth, making phosphorite an essential resource for fertilizer production. Mining for phosphorite is a significant global activity, with major operations in the United States, Morocco, and parts of the Middle East. Understanding phosphorite's geological and ecological roles can provide insights into its importance in agriculture and environmental systems.
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Phosphorite
Phosphorite is a sedimentary rock consisting of at least 50 percent primary or recrystallized phosphate minerals. Phosphorite is sometimes referred to as "phosphate rock." Phosphorite is a relatively rare rock characterized by its unusually high concentration of phosphate, which manifests primarily as the mineral fluorapatite. Phosphorite deposits can be found in various forms. Collections of small lumps of phosphorite can be found on seabed floors around large landmasses. Phosphorite can also accumulate at fossil sites, specifically bone beds, in which phosphate deposits usually contain small amounts of skeletal particles. Finally, phosphorite deposits can occur from phosphatization, a process by which liquids high in phosphate dissolve into sediment.
Overview
Phosphorite is created when sediment is infused with a high concentration of phosphates, the naturally occurring form of the element phosphorus. Phosphorite is most often found on modern seabed floors and within areas of ancient remains. A sedimentary rock is considered a phosphorite when its concentration of phosphorus pentoxide is at least 15.37 percent. Phosphorites have anywhere from one hundred to one thousand times more phosphate content than the average sedimentary rock found on Earth's crust. Phosphorites are classified into three groups based on their relative rates of sediment accumulation and erosion. Pristine phosphate rocks hardly show any signs of erosion and redepositing. Condensed phosphorites are winnowed into concentrated layers as a result of erosion and bioturbulence, or a disturbance caused by living things. Finally, allochthonous phosphorite is formed from sediment deposits that travel from a distance. Rocks become enriched with phosphate in several ways and can be found in terrestrial and marine settings.
On land, phosphorites usually accumulate in areas where fossilized bones and other ancient phosphorus-containing matter exist. Areas known as bone beds contain skeletal and bone fragments that have been winnowed down by processes such as ocean upwelling, which brings deep, nutrient-dense ocean water to the surface, removes the outer sediment, and replaces it with phosphate deposits. As a result, sedimentary layers such as mudrock and limestone are replaced with solid phosphorite.
Marine phosphorites most often occur on the ocean floor in shallow seabeds surrounding large landmasses, called continental shelves. Phosphorus is primarily carried to the ocean floor by rivers as their waters empty into the sea. Other sources of marine phosphorus deposits include precipitation, glacial runoff, dust settlement, cosmic material (such as meteorites), and underground hydrothermal volcanic activity. This phosphorus is then processed and dissolved by tiny organisms known as plankton. When excess organic activity and lack of oxygen occur in a concentrated area—such as when a large group of fish die in a tight space—the bacterial decaying process releases phosphates that replace preceding sediment. Ocean upwelling further deposits phosphate-rich matter that replaces the dissolving sediment.
Phosphorites play an important role in the production of fertilizer phosphate. Phosphorous is a vital ingredient in plant growth and can be found in mass quantities only in phosphorite deposits. Phosphorite mining is a global enterprise and is primarily undertaken in the United States, Morocco, and several regions of the Middle East.
Bibliography
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Glenn, Craig R., and Robert E. Garrison. "Phosphorites." Encyclopedia of Sediments and Sedimentary Rocks. 1st ed., 2005, www.amazon.com/Encyclopedia-Sediments-Sedimentary-Rocks-Sciences/dp/1402008724. Accessed 3 Nov. 2016.
Jasinski, Stephen M. "Phosphate Rock." U.S. Geological Survey, www.minerals.usgs.gov/minerals/pubs/commodity/phosphate‗rock/myb1-2006-phosp.pdf. Accessed 3 Nov. 2016.
"Phosphate." Florida Department of Environmental Protection, 26 Sept. 2022, floridadep.gov/water/mining-mitigation/content/phosphate. Accessed 3 Jan. 2023.
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