Mineral Guide · Mineral

Hydroxylapatite

Hydroxylapatite is a calcium phosphate mineral of the apatite group, occurring in igneous and metamorphic rocks as well as biological materials.

Interactive 3D structure

Crystal structure

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Mineral properties

Formula: Ca₅(PO₄)₃OH
Class: Phosphates
Crystal system: Hexagonal
Typical colours: green, brown, yellow, colourless, white
Lustre: Pearly, Vitreous
Hardness: 5.00
Specific gravity: 3.10-3.20
Crystal habit: Granular, Prismatic, Tabular
Origin: phosphate-rich igneous rocks, carbonatites, metamorphic rocks, caves and biological systems

What is Hydroxylapatite?

Hydroxylapatite is a calcium phosphate mineral of the apatite group, occurring in igneous and metamorphic rocks as well as biological materials.

Mineralogy and structure

Reference formula: Ca₅(PO₄)₃OH. Hydroxylapatite has a hexagonal apatite structure with channels that can host hydroxyl, fluorine or chlorine in related species. Natural composition may be carbonate-rich or otherwise substituted. Hydroxylapatite belongs to the phosphates and has a hexagonal crystal system. Typical hardness is 5–5 on the Mohs scale and specific gravity is approximately 3.1–3.2.

Colour and appearance

Typical colours include colourless, white, green, yellow, brown. The usual prismatic, tabular, granular habit and vitreous, pearly lustre are useful descriptive features, but colour alone is not diagnostic.

Formation and localities

Hydroxylapatite forms in or is associated with phosphate-rich igneous rocks, carbonatites, metamorphic rocks, caves and biological systems. Important documented localities include Brazil, Mexico, Canada, Russia, Norway and the United States.

Collecting and care

Protect crystal faces and keep the geological or biological context recorded; avoid acids.

Sources and editorial review

Reviewed by NotOnlyRocks Editorial Team

Last reviewed: 31 August 2026

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