# Hydroxyapatite
**Hydroxyapatite** (also hydroxylapatite) is a calcium phosphate mineral with the ideal formula Ca₁₀(PO₄)₆(OH)₂, written per formula unit as Ca₅(PO₄)₃OH, that is both an IMA-recognized mineral species and the principal mineral phase of human bone and teeth.[1](https://www.mineralogist.org/m/hydroxylapatite) • [2](https://health.ec.europa.eu/system/files/2023-03/sccs_o_269.pdf) Synthetic hydroxyapatite with a calcium-to-phosphorus ratio of 1.67, matching the mineral of natural hard tissue, is used as bone scaffold, bone filler, implant coating, and drug-delivery material.[3](https://www.mdpi.com/1422-0067/24/6/5576) The name descends from the generic term *apatite*, introduced by Abraham Gottlob Werner in 1786 from the Greek *apatao*, "to deceive", because early mineralogists misidentified the mineral as aquamarine, chrysolite, amethyst, fluor, schorl, and other species.[4](https://fmm.ru/images/5/53/Pasero2010.pdf) • [5](https://www.jstage.jst.go.jp/article/jhtb/24/2/24_111/_pdf)
| Key fact | Detail |
|---|---|
| Formula | Ca₁₀(PO₄)₆(OH)₂; Ca/P atomic ratio 1.67; molar mass 502.31 g/mol[2](https://health.ec.europa.eu/system/files/2023-03/sccs_o_269.pdf) • [6](https://jkk.unjani.ac.id/index.php/jkk/article/download/1101/174) |
| Crystal structure | Hexagonal, space group P6₃/m; OH⁻ ions occupy channels along the c axis between two distinct calcium sites[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC7116284/) |
| Physical properties | Mohs hardness 5; specific gravity 3.14–3.21[1](https://www.mineralogist.org/m/hydroxylapatite); melting point 1614 °C[8](https://www.mdpi.com/2571-6131/4/4/39) |
| Solubility | Practically insoluble in water (0.0065 g/L at 20 °C), soluble at low pH[2](https://health.ec.europa.eu/system/files/2023-03/sccs_o_269.pdf) |
| Biological share | 70–80% of the weight of dentin and enamel[9](https://www.ncbi.nlm.nih.gov/books/NBK513314/) |
| Market | USD 2,540.0 million in 2024, projected USD 3,915.3 million by 2030 (7.5% CAGR)[10](https://www.grandviewresearch.com/horizon/outlook/hydroxyapatite-market-size/global) |
| SCCS-assessed safe-use concentrations for nano-hydroxyapatite | Up to 29.5% in toothpaste and 10% in mouthwash under the Submission IV opinion[11](https://health.ec.europa.eu/publications/sccs-scientific-opinion-hydroxyapatite-nano-submission-iv_en) |
## Crystal structure and chemistry
The apatite archetype is a hexagonal structure with space group P6₃/m and unit-cell parameters a = 9.3–9.6 Å and c = 6.7–6.9 Å.[4](https://fmm.ru/images/5/53/Pasero2010.pdf) For hydroxyapatite specifically, one review gives a = b = 9.4225 Å and c = 6.8850 Å,[8](https://www.mdpi.com/2571-6131/4/4/39) while another gives a = 9.432 Å and c = 6.881 Å.[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC7116284/) Calcium, phosphate, and hydroxyl ions make up 39.84, 56.77, and 3.39 wt.% of the compound respectively.[8](https://www.mdpi.com/2571-6131/4/4/39)
The hydroxyl channels define the lattice. OH⁻ ions and four Ca²⁺ ions at Ca(1) sites lie along columns parallel to the c axis, while six Ca²⁺ ions at Ca(2) sites form triangles around the OH⁻ groups.[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC7116284/) The calcium tunnel holding the OH ions is the site most easily substituted by fluoride.[5](https://www.jstage.jst.go.jp/article/jhtb/24/2/24_111/_pdf) More broadly, ionic substitution occurs at three crystallographic sites: calcium sites (for example Sr²⁺, Mg²⁺), phosphate sites (CO₃²⁻, HPO₄²⁻), and hydroxyl sites (F⁻, Cl⁻, CO₃²⁻).[6](https://jkk.unjani.ac.id/index.php/jkk/article/download/1101/174)
## Physical and chemical properties
The mineral has a Mohs hardness of 5 and a specific gravity of 3.14–3.21; it is typically white, colorless, or gray with a white streak and a vitreous to subresinous or earthy luster.[1](https://www.mineralogist.org/m/hydroxylapatite) Its water solubility is 0.0065 g/L at 20 °C, but it dissolves at low pH.[2](https://health.ec.europa.eu/system/files/2023-03/sccs_o_269.pdf) That acid sensitivity contributes to tooth decay: acid attack dissolves tooth-enamel apatite.[5](https://www.jstage.jst.go.jp/article/jhtb/24/2/24_111/_pdf)
Dense hydroxyapatite ceramic has a tensile strength of 38–300 MPa, a [Young's modulus](https://www.edgepedia.org/youngs-modulus) of 35–120 GPa, and a fracture toughness of 0.7–1.2 MPa·m½ that decreases with porosity; it melts at 1614 °C.[8](https://www.mdpi.com/2571-6131/4/4/39) Reported compressive strength ranges differ between references, 120–150 MPa in one clinical source and 120–900 MPa in a ceramics review.[9](https://www.ncbi.nlm.nih.gov/books/NBK513314/) • [8](https://www.mdpi.com/2571-6131/4/4/39) A Weibull modulus of 5–18 indicates brittleness.[9](https://www.ncbi.nlm.nih.gov/books/NBK513314/)
## Biological role in bone and teeth
Hydroxyapatite constitutes 70% to 80% of the weight of dentin and enamel. Enamel crystals measure about 25 nm thick, 40 to 120 nm wide, and 160 to 1000 nm long.[9](https://www.ncbi.nlm.nih.gov/books/NBK513314/)
Biological apatite is not the stoichiometric mineral. Bone and tooth mineral is calcium-deficient (Ca/P below 1.67), composed of small, poorly crystalline, highly soluble carbonated apatite crystals that carry vicarious ions including F⁻, Cl⁻, SiO₄⁴⁻, and CO₃²⁻ among the anions and Na⁺, Mg²⁺, K⁺, Sr²⁺, Zn²⁺, Ba²⁺, and Al³⁺ among the cations.[12](https://link.springer.com/rwe/10.1007/978-3-319-12460-5_7) Substitution changes solubility in a consistent direction: magnesium, carbonate, or strontium increase solubility, while fluoride reduces it.[9](https://www.ncbi.nlm.nih.gov/books/NBK513314/) Synthetic carbonate apatite with 12 wt.% carbonate can be sintered at 600–750 °C and retains about 6 wt.% carbonate in the lattice, comparable to bone apatite.[8](https://www.mdpi.com/2571-6131/4/4/39) This carbonated, low-crystallinity character is what motivates carbonate-substituted hydroxyapatite synthesis for bone grafting.[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC7116284/)
## Natural occurrence, mining, and industrial grades
Apatite is the industrial source of phosphate. Global phosphate rock production was approximately 444 million tons in 2024, up 2.8% year over year, with China the largest producer at 303 million tons (68% of volume), [Morocco](https://www.edgepedia.org/morocco) second at 31 million tons, and the United States third at 27 million tons (6%).[13](https://www.indexbox.io/blog/phosphate-rock-world-market-overview-2024-1/) Consumption rose to 450 million tons in 2024, up 3.5% on 2023.[13](https://www.indexbox.io/blog/phosphate-rock-world-market-overview-2024-1/)
Grade follows end use. Much mined apatite serves mainly as a source of phosphate and other phosphorus-containing compounds, while much purer synthetic material is used to form artificial teeth and bones or repair natural tissues.[14](https://www.acs.org/molecule-of-the-week/archive/h/hydroxyapatite.html) Mined phosphate rock requires purification to remove trace metals for biomedical use, and biomedical-grade calcium can also come from high-purity chemical salts or bio-waste streams such as eggshells and marine shells.[15](https://www.mordorintelligence.com/industry-reports/hydroxyapatite-market)
## Synthetic production and biomedical applications
Synthetic routes are well established. Wet precipitation yields nano-sized particles of low-to-moderate crystallinity, sol-gel gives high phase purity, hydrothermal synthesis gives highly crystalline well-defined morphology, and microwave-assisted synthesis offers rapid uniform heating with controlled particle size.[6](https://jkk.unjani.ac.id/index.php/jkk/article/download/1101/174) The solid-state method requires raw materials with a Ca/P ratio of 1.67, ball-milled for uniform particle size.[9](https://www.ncbi.nlm.nih.gov/books/NBK513314/) Typical sintering uses heating rates of 0.5–3 °C/min, temperatures of 1000–1250 °C, and holding times of 2–5 h.[8](https://www.mdpi.com/2571-6131/4/4/39) Most commercially available hydroxyapatite is sintered at 900 °C or above, which yields a low specific surface area of 2–5 m²/g, reduced bioactivity, and poor solubility.[3](https://www.mdpi.com/1422-0067/24/6/5576)
**Implant coatings and scaffolds.** Coating bone implants with hydroxyapatite is one of the most used techniques because of its biocompatibility and osteoconductive (provides a scaffold for new bone growth) behavior.[7](https://pmc.ncbi.nlm.nih.gov/articles/PMC7116284/) Coatings are applied to titanium alloys by plasma spray, HVOF, electrochemical deposition, or sputtering.[16](https://www.qyresearch.com/reports/5492829/hydroxyapatite) Thick plasma-sprayed coatings, however, can crack and delaminate and are scarcely uniform, so research pushes toward coatings closer to bone apatite and toward alternative plasma-assisted deposition with better adhesion and compositional control.[17](https://iris.unimo.it/retrieve/47315477-388b-4487-a897-210e2c57713c/coatings-08-00269-v2.pdf) Hydroxyapatite is also used as a drug carrier in drug and gene delivery systems.[18](https://pubs.rsc.org/en/content/articlelanding/2017/ra/c6ra26124h) Pristine nano-hydroxyapatite as slurry or powder has insufficient mechanical strength and slow degradation, so it is commonly combined with metals, polymers, and bioceramics.[19](https://academic.oup.com/rb/article/doi/10.1093/rb/rbae129/7876291) Sustainable calcium precursors under investigation include eggshells, fish bones and scales, algal biomass, mollusk shells, and limestone.[6](https://jkk.unjani.ac.id/index.php/jkk/article/download/1101/174)
**Dental use.** Nano-hydroxyapatite penetrates the enamel surface to replace lost phosphate and calcium ions, remineralizing damaged enamel, and forms a protective coating over exposed dentinal tubules to reduce hypersensitivity.[9](https://www.ncbi.nlm.nih.gov/books/NBK513314/) It is also consolidated into chromatographic media for life-science separations.[16](https://www.qyresearch.com/reports/5492829/hydroxyapatite)
## By the numbers
In 2024, the worldwide hydroxyapatite market was valued at USD 2,540.0 million, and by 2030 it is expected to grow to USD 3,915.3 million, representing a 7.5% CAGR between 2025 and 2030.[10](https://www.grandviewresearch.com/horizon/outlook/hydroxyapatite-market-size/global) Nano-sized hydroxyapatite generated USD 1,240.0 million of that 2024 revenue and is the fastest-growing type segment; Asia Pacific was the largest revenue region, North America accounted for 17.0%, and India is projected to reach USD 596.0 million by 2030.[10](https://www.grandviewresearch.com/horizon/outlook/hydroxyapatite-market-size/global) Global production reached approximately 23 metric tons in 2024 at an average market price of around US$3,526 per kg.[16](https://www.qyresearch.com/reports/5492829/hydroxyapatite)
## How it compares with fluorapatite and other calcium phosphates
The apatite group has the general formula M₁₀(XO₄)₆Z₂ with wide substitution; hydroxyapatite Ca₁₀(PO₄)₆(OH)₂ and fluorapatite Ca₁₀(PO₄)₆F₂ form a perfect solid-solution system.[5](https://www.jstage.jst.go.jp/article/jhtb/24/2/24_111/_pdf) [Fluorapatite](https://www.edgepedia.org/fluorapatite) and chlorapatite are the anion-substituted analogs in which OH⁻ is replaced by F⁻ and Cl⁻ respectively.[8](https://www.mdpi.com/2571-6131/4/4/39)
Fluoride substitution lowers solubility. In bone tissue engineering this is a drawback: fluorapatite has greater chemical stability and a lower bioresorption rate than hydroxyapatite, hindering its replacement with newly formed tissue after implantation.[3](https://www.mdpi.com/1422-0067/24/6/5576) In one comparative in vitro test, a fluorapatite scaffold released significantly more Ca²⁺ than hydroxyapatite in both PBS (pH 7.4) and HCl (pH 4.5) at most time points, except after 30 days in HCl where hydroxyapatite released more calcium.[3](https://www.mdpi.com/1422-0067/24/6/5576) Direct dissolution and solubility measurements of the two end-members have been made at 25 °C and 45 °C to quantify this difference.[20](https://www.sciencedirect.com/science/article/abs/pii/S0009254109003398) Hydroxyapatite sits within a wider family of biomedical calcium phosphates that includes tetracalcium phosphate, alpha and beta tricalcium phosphate, fluorapatite, dicalcium phosphate anhydrous, and amorphous calcium phosphate.[21](https://pubs.rsc.org/en/content/articlelanding/2024/tb/d3tb02846a)
## Recent developments
**Regulation of nano-hydroxyapatite in cosmetics.** In March 2023 the EU Scientific Committee on Consumer Safety (SCCS) concluded that hydroxyapatite (nano) is safe at up to 10% in toothpaste and up to 0.465% in mouthwash, limited to rod-shaped, uncoated particles with at least 95.8% having an aspect ratio below 3.[2](https://health.ec.europa.eu/system/files/2023-03/sccs_o_269.pdf) A later opinion (Submission IV) considered hydroxyapatite (nano) safe at concentrations up to 29.5% in toothpaste and 10% in mouthwash, for rod-shaped uncoated particles of which at least 87% have aspect ratios of 3 or less and the remaining 13% do not exceed 9.[11](https://health.ec.europa.eu/publications/sccs-scientific-opinion-hydroxyapatite-nano-submission-iv_en) That opinion found no mutagenic hazard, cytotoxicity, or inflammatory effects even at high concentrations in a buccal mucosa cell model, and noted that ingested nanoparticles dissolve rapidly in gastric fluid.[11](https://health.ec.europa.eu/publications/sccs-scientific-opinion-hydroxyapatite-nano-submission-iv_en) In 2024, EU Regulation 2024/858 set limits on nano-hydroxyapatite in toothpaste and mouthwash, while the SCCS raised concerns about aerosolized nano-hydroxyapatite as a potential inhalation hazard.[15](https://www.mordorintelligence.com/industry-reports/hydroxyapatite-market) In 2025, two European startups abandoned their nano-hydroxyapatite initiatives after insurers refused liability coverage.[15](https://www.mordorintelligence.com/industry-reports/hydroxyapatite-market)
**Clinical evidence on nano-hydroxyapatite toothpaste.** A 24-month randomised clinical trial enrolled 610 children aged 4–5 and 6–7 years, comparing two fluoride-substituted hydroxyapatite toothpastes (HAF1000 and HAF1450, at 1000 and 1450 ppm F) against two monofluorophosphate toothpastes at the same fluoride levels.[22](https://pmc.ncbi.nlm.nih.gov/articles/PMC11287134/) At trial end, both HAF groups showed statistically significantly lower levels of the primary cariogenic bacteria ([Streptococcus mutans](https://www.edgepedia.org/streptococcus-mutans), S. sobrinus, [Lactobacillus](https://www.edgepedia.org/lactobacillus) casei, and L. fermentum) than the fluoride groups (P = .03), and the minimum plaque pH after sucrose challenge increased most in the HAF groups.[22](https://pmc.ncbi.nlm.nih.gov/articles/PMC11287134/) The authors characterize the evidence as robust but still inconclusive for reducing caries risk factors and preventing caries lesions.[22](https://pmc.ncbi.nlm.nih.gov/articles/PMC11287134/)
For dentin hypersensitivity, a systematic review and meta-analysis of 13 randomized controlled trials involving 609 patients found that nano-hydroxyapatite toothpaste produced greater short-term (2-week) reductions in visual analog scale pain scores than fluoride toothpaste (SMD = 8.81, 95% CI [0.31, 17.30], p = 0.0017).[23](https://link.springer.com/article/10.1186/s12903-026-09293-4) At 8-week follow-up, however, fluoride demonstrated superior efficacy for cold air sensitivity (SMD = 0.35, 95% CI [0.05, 0.65], p = 0.02), and subgroup analysis found nano-hydroxyapatite at 15%–20% concentration produced the optimal effect (SMD = −0.77, 95% CI [−1.16, −0.39], p < 0.0001) with low heterogeneity (I² = 11%).[23](https://link.springer.com/article/10.1186/s12903-026-09293-4)
**Biomaterials.** Translating nano-hydroxyapatite composites into clinical use is identified as requiring advanced biocompatibility screening, consistent manufacturing techniques such as 3D printing, and proactive regulatory engagement.[19](https://academic.oup.com/rb/article/doi/10.1093/rb/rbae129/7876291)
## History
Apatite was first recognized as a mineral species, and named, in 1786 by Abraham Gottlob Werner (1750–1817), known as "the father of German geology".[24](https://www.sciencedirect.com/science/article/pii/S0928493113002166) Apatites include hydroxyapatite, fluorapatite, and oxyapatite.[24](https://www.sciencedirect.com/science/article/pii/S0928493113002166) Biomedical milestones followed in the twentieth century: the first study of calcium phosphates as bone-substitute filler dates to 1920, when they were used to repair critical-size bone defects in rabbits; in 1969 Levitt et al. wrote one of the first papers on hydroxyapatite for implants in contact with bone; and in 1979 hydroxyapatite cylinders were used for tooth replacement, followed in the early 1980s by hydroxyapatite blocks and coatings to enhance bone fixation in restorative dental procedures.[8](https://www.mdpi.com/2571-6131/4/4/39) • [9](https://www.ncbi.nlm.nih.gov/books/NBK513314/)
## References
1. [Hydroxylapatite Properties, Formula & Mineral Information, Mineralogist.org](https://www.mineralogist.org/m/hydroxylapatite)
2. [SCCS Final Opinion on Hydroxyapatite (nano), SCCS O-269 (March 2023), European Commission](https://health.ec.europa.eu/system/files/2023-03/sccs_o_269.pdf)
3. [Hydroxyapatite or Fluorapatite—Which Bioceramic Is Better as a Base for the Production of Bone Scaffold?, Int. J. Mol. Sci. (MDPI)](https://www.mdpi.com/1422-0067/24/6/5576)
4. [Nomenclature of the apatite supergroup minerals, IMA report](https://fmm.ru/images/5/53/Pasero2010.pdf)
5. [Historical Review of Biological Apatite Crystallography, Japanese Journal of Hard Tissue Biology](https://www.jstage.jst.go.jp/article/jhtb/24/2/24_111/_pdf)
6. [Hydroxyapatite as a Biomimetic Alternative to Fluoride in Toothpaste Formulations: A Review](https://jkk.unjani.ac.id/index.php/jkk/article/download/1101/174)
7. [Substituted hydroxyapatite coatings of bone implants, Journal of Materials Chemistry B](https://pmc.ncbi.nlm.nih.gov/articles/PMC7116284/)
8. [Hydroxyapatite for Biomedical Applications: A Short Overview, Ceramics (MDPI)](https://www.mdpi.com/2571-6131/4/4/39)
9. [Hydroxyapatite Dental Material, StatPearls, NCBI Bookshelf](https://www.ncbi.nlm.nih.gov/books/NBK513314/)
10. [Hydroxyapatite Market Size & Outlook, 2030, Grand View Research](https://www.grandviewresearch.com/horizon/outlook/hydroxyapatite-market-size/global)
11. [SCCS Scientific Opinion on Hydroxyapatite (nano) – Submission IV, European Commission](https://health.ec.europa.eu/publications/sccs-scientific-opinion-hydroxyapatite-nano-submission-iv_en)
12. [Cationic and Anionic Substitutions in Hydroxyapatite, Springer reference-work chapter](https://link.springer.com/rwe/10.1007/978-3-319-12460-5_7)
13. [Worldwide Phosphate Rock Market Overview 2024, IndexBox](https://www.indexbox.io/blog/phosphate-rock-world-market-overview-2024-1/)
14. [Hydroxyapatite, Molecule of the Week, American Chemical Society](https://www.acs.org/molecule-of-the-week/archive/h/hydroxyapatite.html)
15. [Hydroxyapatite Market, Mordor Intelligence](https://www.mordorintelligence.com/industry-reports/hydroxyapatite-market)
16. [Hydroxyapatite – Global Market Share and Ranking, QY Research](https://www.qyresearch.com/reports/5492829/hydroxyapatite)
17. [A Review on Ionic Substitutions in Hydroxyapatite Thin Films, Coatings (2018)](https://iris.unimo.it/retrieve/47315477-388b-4487-a897-210e2c57713c/coatings-08-00269-v2.pdf)
18. [Recent advances in the synthesis, functionalization and biomedical applications of hydroxyapatite, RSC Advances](https://pubs.rsc.org/en/content/articlelanding/2017/ra/c6ra26124h)
19. [Advancements in nanohydroxyapatite: synthesis, biomedical applications and composite developments, Regenerative Biomaterials (2024)](https://academic.oup.com/rb/article/doi/10.1093/rb/rbae129/7876291)
20. [A comparative study on the dissolution and solubility of hydroxylapatite and fluorapatite at 25 °C and 45 °C, Chemical Geology](https://www.sciencedirect.com/science/article/abs/pii/S0009254109003398)
21. [Synthesis of pure and doped nano-calcium phosphates using different conventional methods for biomedical applications: a review, Journal of Materials Chemistry B (2024)](https://pubs.rsc.org/en/content/articlelanding/2024/tb/d3tb02846a)
22. [Effects of Hydroxyapatite-Containing Toothpastes on Some Caries-Related Variables: A Randomised Clinical Trial](https://pmc.ncbi.nlm.nih.gov/articles/PMC11287134/)
23. [Efficacy comparison of nano-hydroxyapatite and fluoride for dentin hypersensitivity: a systematic review and meta-analysis, BMC Oral Health](https://link.springer.com/article/10.1186/s12903-026-09293-4)
24. [A detailed history of calcium orthophosphates from 1770s till 1950](https://www.sciencedirect.com/science/article/pii/S0928493113002166)
---
*Topic: Encyclopedia › Physical world and mathematics › Earth sciences › Geology and mineralogy › Mineralogy and minerals › Ore and industrial minerals*
*Initially written Sep 17, 2026 · Reviewed: Oct 15, 2026 · Edited: Oct 15, 2026 · Last review: Oct 15, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license