Calcium Hydroxyphosphate

Calcium hydroxyphosphate (calcium phosphate tribasic, tribasic calcium phosphate, hydroxyapatite, HAp) is an inorganic chemical compound that is made up of calcium, hydrogen, oxygen and phosphorus. Its formula is Ca5(OH)(PO4)3. It is a naturally occurring mineral form of calcium apatite. It’s a major component of bone and teeth in humans and other vertebrates.

It also known as hydroxyapatite, is a naturally occurring mineral form of calcium apatite with the formula: Ca10(PO4)6(OH)2. It is a major component of bones and teeth in vertebrates and is also found in some pathological calcifications like kidney stones and arterial plaques. It is found in the body and as the mineral hydroxyapatite.

Properties

Molar Mass: 1004.6 g/mol
Solubility: Slightly soluble in water; more soluble in acidic environments
Crystal System: Hexagonal
pH Stability: Stable in neutral to basic pH, dissolves in acidic conditions
Decomposes: At high temperatures to tricalcium phosphate and calcium oxide
Color: White or pale yellow
Density: ~3.1 g/cm³
Hardness: ~5 on Mohs scale
Structure: Crystalline, hexagonal unit cell
Thermal Stability: Stable up to ~1,100°C

Natural Occurrence

1. Biological Systems

Bones and Teeth: Main inorganic component (up to 70% by weight in bones, 96% in enamel).
Dental Plaque: Can form via mineralization.
Pathological Calcifications: Appears in kidney stones, gallstones, and arterial plaques.

2. Geological Sources

Mineral Form: Apatite group, especially hydroxyapatite.
Found in phosphate rock deposits (often mixed with fluorapatite and chlorapatite).
Locations: Morocco, Russia, USA, and other phosphate-rich geological areas.

Uses and Applications