The Phosphoria Formation of the western United States is a geological formation of Early Permian age. It represents some 15 million years of sedimentation, reaches a thickness of 420 metres (1,380 ft) and covers an area of 350,000 square kilometres (140,000 sq mi).
An outcrop of the Phosphoria Formation near the Big Hole River in western Montana.
Tooth whorl of Helicoprion from the Phosphoria Formation
A phosphorite mine near Flaming Gorge, Utah, in 2008.
Peloidal phosphorite from the Phosphoria Formation, Simplot Mine, Idaho. 4.6 cm wide.
Phosphorite, phosphate rock or rock phosphate is a non-detrital sedimentary rock that contains high amounts of phosphate minerals. The phosphate content of phosphorite (or grade of phosphate rock) varies greatly, from 4% to 20% phosphorus pentoxide (P2O5). Marketed phosphate rock is enriched ("beneficiated") to at least 28%, often more than 30% P2O5. This occurs through washing, screening, de-liming, magnetic separation or flotation. By comparison, the average phosphorus content of sedimentary rocks is less than 0.2%.
Peloidal phosphorite, Phosphoria Formation, Simplot Mine, Idaho. 4.6 cm wide.
Fossiliferous peloidal phosphorite, (4.7 cm across), Yunnan Province, China.
Guano phosphorite mining in the Chincha Islands of Peru, c. 1860
Phosphorite mine near Oron, Negev, Israel.