is a glassy precipitate of variable composition that may be present in biological systems.

Di- and polyphosphates

These materials contain Ca²⁺ combined with the polyphosphates, such as {{chem and triphosphate :
* Dicalcium diphosphate (CAS#7790-76-3]: Ca₂P₂O₇
* Calcium triphosphate (CAS# 26158-70-3): Ca₅(P₃O₁₀)₂