Black phosphorite nodule from the Precambrian of Ukraine. (5.7 centimeters across)

Phosphorites are calcium phosphate-rich sedimentary rocks, generally considered to have >15-20% phosphate content. Texturally, phosphorites can be obviously granular, with fossil fragments or oolites or peloids or lithic fragments, or they can be composed of extremely fine-grained, phosphate-rich mud. Compositionally, the phosphate component in phosphorites is principally a mix of apatite minerals: chlorapatite (Ca5(PO4)3Cl), fluorapatite (Ca5(PO4)3F), hydroxyapatite (Ca5(PO4)3OH)), and carbonate fluorapatite (Ca10(PO4,CO3)6F2-3).

Phosphorites are generally marine sedimentary rocks. They range in age from Precambrian to Holocene. In modern oceans, they tend to occur along the eastern margins of some ocean basins where deep-water upwelling occurs under areas of high biologic productivity.

Stratigraphy: Kalyus Member (Kalus Member; Kallyusa Member), Nagoryany Formation, Mogilev-Podolsky Series, upper Ediacaran, near-uppermost Neoproterozoic