Description
Phosphorite, or phosphate rock, is a sedimentary rock composed of at least 20% phosphate. Phosphorite has the same internal structure and texture as fine-grained limestone and is often the result of diagenetic alteration of limestone, in which carbonate is replaced by phosphate. This diagenetic alteration requires large amounts of phosphate in the groundwater, such as near large guano deposits. The phosphate is usually a form of fluorapatite, for example, with a carbonate and hydroxyl group (Ca10(PO4CO3)F2-3), and forms masses of very small crystals (cryptocrystalline masses, grain size <1 μm) called rosin.
