fosfaatskeletjes

Fosfaatskeletjes are microscopic shells composed mainly of calcium phosphate minerals that occur in aquatic sediments and soils. They form through biomineralization by phosphate-accumulating organisms and by abiotic precipitation under conditions of elevated phosphate and calcium ion availability. In geochemical literature they are described as discrete, shell-like particles that can encapsulate organic matter or microorganisms.

Chemically, fosfaatskeletjes are often crystalline hydroxyapatite (Ca5(PO4)3(OH)) or fluorapatite, and less commonly amorphous calcium phosphate. Nucleation is promoted by organic macromolecules, extracellular polymers, and mineral surfaces. Environmental factors such as pH around neutral to mildly alkaline, high phosphate concentration, and adequate calcium levels favor their precipitation. They may grow attached to organic debris or exist as isolated grains in sediments and pore waters.

They are reported from coastal marine sediments, continental shelf deposits, and freshwater sediments where phosphate is relatively abundant. In the sedimentary record, fosfaatskeletjes can contribute to phosphorite-rich intervals and serve as indicators of historical phosphate availability and biogeochemical conditions. They also play a role in the long-term sequestration of phosphorus, potentially delaying its return to the water column under burial.

Analytical approaches include scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), X-ray diffraction (XRD), and infrared spectroscopy (FTIR) to identify composition and crystallinity. Their study informs models of phosphorus cycling, diagenesis, and paleoenvironmental reconstruction.

Further research addresses their diversity, seasonal formation, and potential as a mineral resource, as well as their response to eutrophication and climate-driven changes in phosphorus availability.