brushite

Brushite is a calcium phosphate mineral with the chemical formula CaHPO4·2H2O. It is a calcium phosphate dihydrate and is of interest in geology and biomaterials. It commonly occurs as a secondary phase in phosphate-rich sedimentary rocks, forming through diagenetic alteration of phosphatic nodules, bone-derived phosphates, or guano in caves. In the field it is often found with other phosphates such as apatite and whitlockite and can occur in hydrothermal veins.

Crystals of brushite are typically colorless to white and have a vitreous to silky luster. They form tabular or prismatic crystals but more often present as microscopic grains or fibrous aggregates. Brushite has a relatively low hardness on the Mohs scale, about 3.5 to 4, and is soluble in acids. It is more soluble than hydroxyapatite, which contributes to its tendency to transform to more stable phosphate phases under changing conditions.

Formation and transformation: Brushite is metastable at ordinary temperatures and can convert to hydroxyapatite or whitlockite over time or under shifts in pH and temperature. In biological contexts, brushite can appear transiently during bone and dental mineralization and is recognized as an intermediate phase in the diagenesis of bones and guano.

Uses: In biomedicine, brushite is used in calcium phosphate cements that set in situ and can transform to hydroxyapatite as part of bone repair materials. The mineral is also studied as a paleoenvironmental indicator of phosphate-rich conditions.