Hydroxyapatite (bone mineral bioceramic) HA

spore: profile
id: hydroxyapatite
spore_version: 0.2
family: calcium-phosphate
name: Hydroxyapatite (bone mineral bioceramic)
abbreviation: HA
role: bioceramic (bone-mineral analogue)
category: living
type: bio-grown-building-materials
summary: |
  Hydroxyapatite (HA, Ca10(PO4)6(OH)2) is the calcium phosphate mineral of bone. The NIST reference powder SRM 2910 has a Ca/P molar ratio of 1.664 ± 0.005 and a hexagonal unit cell with a = 0.94238 ± 0.00009 nm and c = 0.68854 ± 0.00006 nm (Markovic et al., 2004). Measured specific gravity is 3.14 to 3.21 and Mohs hardness is 5 (Wikipedia infobox). No strength or stiffness value for dense sintered HA is recorded in this profile.
best_for: Calcium phosphate work where composition and crystal structure must be documented (NIST reference powder SRM 2910)
weakest_at: 'Mechanical strength and stiffness: no modulus, hardness or strength value for dense sintered HA is recorded in this profile'
identity:
  formula: Ca10(PO4)6(OH)2 (two formula units per unit cell, as written on the Wikipedia page)
  cas: 1306-06-5
  crystal_system: hexagonal
  space_group: P63/m
  source: wiki-ha
  where: 'Infobox (Identification): crystal system hexagonal, space group P63/m, Z = 2; formula in the Lead section. CAS number from PubChem CID 14781 (source pubchem-ha).'
tags:
  environments: []
  stresses: []
  applications:
    - structures
properties:
  - benchmark: ca_p_molar_ratio
    label: Calcium-to-phosphorus molar ratio, SRM 2910 powder
    value: 1.664
    unit: '-'
    scope: material
    conditions:
      material: HA reference powder SRM 2910, precipitated
      basis: mean Ca and total P contents
      uncertainty: ± 0.005 as printed
    method: Calculated by the authors from mean Ca and total P contents (Section 3.1.3). The independent thermal-product check gave 1.6649 ± 0.0005 (not recorded here).
    status: ground
    source: markovic2004
    where: Section 3.1.3
  - benchmark: lattice_parameter_a
    label: Unit-cell parameter a, SRM 2910 powder
    value: 0.94238
    unit: nm
    scope: material
    conditions:
      material: HA-SRM powder
      method_as_printed: Standard
      uncertainty: ± 0.00009, expanded U as printed
    method: Unit-cell parameter from the authors' own analysis, row HA-SRM Standard in Table 6. Other rows of the same table give Rietveld values from other work.
    status: ground
    source: markovic2004
    where: Table 6, row HA-SRM (Standard)
  - benchmark: lattice_parameter_c
    label: Unit-cell parameter c, SRM 2910 powder
    value: 0.68854
    unit: nm
    scope: material
    conditions:
      material: HA-SRM powder
      method_as_printed: Standard
      uncertainty: ± 0.00006, expanded U as printed
    method: Unit-cell parameter from the authors' own analysis, row HA-SRM Standard in Table 6.
    status: ground
    source: markovic2004
    where: Table 6, row HA-SRM (Standard)
  - benchmark: bet_surface_area
    label: BET specific surface area, precipitated SRM 2910 powder
    value: 18.3
    unit: m2/g
    scope: material
    conditions:
      material: precipitated HA-SRM powder
      adsorbate: N2
      uncertainty: ± 0.3 m2/g as printed
      samples: mean of 12 samples; individual samples 17.7 to 19.1 m2/g
    method: BET nitrogen adsorption, mean of 12 samples as printed in Section 3.2
    status: ground
    source: markovic2004
    where: Section 3.2
  - benchmark: solubility_product
    label: Solubility product of HA (Ksp)
    value: 2.03e-59
    unit: '-'
    scope: material
    conditions:
      temperature: 37.0 ± 0.1 °C
      equilibration: 60 days in phosphoric acid
      uncertainty: ± 0.71e-59, expanded uncertainty with U = 2uc as printed
    method: Saturated-solution measurement. The paper also gives pKsp 58.69 ± 0.15. No unit is printed for Ksp, so the unit is entered as -.
    status: ground
    source: markovic2004
    where: Section 3.9
  - benchmark: thermal_mass_loss
    label: Total mass loss on heating, SRM 2910 powder
    value: 1.7
    unit: '%'
    scope: material
    conditions:
      atmosphere: nitrogen (N2)
      temperature_range: 30 to 900 °C
      heating_rate: 10 °C/min
      uncertainty: ± 0.05 % as printed
    method: Thermogravimetry. The paper reports no decomposition temperature for hydroxyapatite itself.
    status: ground
    source: markovic2004
    where: Sections 2.3.3 and 3.1.5 (thermogravimetry)
  - benchmark: mass_fraction_calcium
    label: Calcium (Ca2+) mass fraction, SRM 2910 unit cell
    value: 39.15
    unit: '%'
    scope: material
    conditions:
      material: HA-SRM, mass fraction per unit cell
      uncertainty: ± 0.10 %
    method: Chemical composition table (Table 1, Ca2+ row, n = 20 as printed)
    status: ground
    source: markovic2004
    where: Table 1, Ca2+ row
  - benchmark: mass_fraction_phosphate
    label: Phosphate (PO4 3-) mass fraction, SRM 2910 unit cell
    value: 55.16
    unit: '%'
    scope: material
    conditions:
      material: HA-SRM, mass fraction per unit cell
      uncertainty: ± 0.15 %
    method: Chemical composition table (Table 1, PO4 3- row, n = 20 as printed)
    status: ground
    source: markovic2004
    where: Table 1, PO4 3- row
  - benchmark: mass_fraction_water
    label: Water (H2O) mass fraction, SRM 2910 unit cell
    value: 1.59
    unit: '%'
    scope: material
    conditions:
      material: HA-SRM, mass fraction per unit cell
      uncertainty: ± 0.05 %
    method: Chemical composition table (Table 1, H2O row, n = 5 as printed)
    status: ground
    source: markovic2004
    where: Table 1, H2O row
  - benchmark: particle_height
    label: Crystal height, SRM 2910 powder
    value: 0.1
    value_high: 0.3
    bound: range
    unit: μm
    scope: material
    conditions:
      form: cylindrical crystals of precipitated HA-SRM powder
      method_as_printed: TEM and SEM
    method: Range printed with the approximate sign in Section 3.2
    status: ground
    source: markovic2004
    where: Section 3.2
  - benchmark: particle_diameter
    label: Crystal diameter, SRM 2910 powder
    value: 0.05
    value_high: 0.15
    bound: range
    unit: μm
    scope: material
    conditions:
      form: cylindrical crystals of precipitated HA-SRM powder
      method_as_printed: TEM and SEM
    method: Range printed with the approximate sign in Section 3.2
    status: ground
    source: markovic2004
    where: Section 3.2
  - benchmark: specific_gravity
    label: Specific gravity, measured
    value: 3.14
    value_high: 3.21
    bound: range
    unit: '-'
    scope: material
    conditions:
      basis: measured value as printed in the infobox; form and test not stated
    method: Infobox value printed as 3.14–3.21 (measured). The page prints no unit; specific gravity is dimensionless.
    status: ground
    source: wiki-ha
    where: Infobox (Identification), Specific gravity row
  - benchmark: specific_gravity
    label: Specific gravity, calculated
    value: 3.16
    unit: '-'
    scope: material
    conditions:
      basis: calculated value as printed in the infobox
    method: Infobox value marked as calculated by the source
    status: calculated
    source: wiki-ha
    where: Infobox (Identification), Specific gravity row
  - benchmark: mohs_hardness
    label: Mohs scale hardness
    value: 5
    unit: '-'
    scope: material
    conditions:
      basis: mineral hardness as printed in the infobox; no test method stated
    method: Infobox value, Mohs scale hardness row
    status: ground
    source: wiki-ha
    where: Infobox (Identification), Mohs scale hardness row
  - benchmark: refractive_index
    label: Refractive index, nω
    value: 1.651
    unit: '-'
    scope: material
    conditions:
      basis: optical value printed for the mineral; wavelength not stated on the page
    method: Infobox value, refractive index row
    status: ground
    source: wiki-ha
    where: Infobox (Identification), Refractive index row
  - benchmark: refractive_index
    label: Refractive index, nε
    value: 1.644
    unit: '-'
    scope: material
    conditions:
      basis: optical value printed for the mineral; wavelength not stated on the page
    method: Infobox value, refractive index row
    status: ground
    source: wiki-ha
    where: Infobox (Identification), Refractive index row
  - benchmark: birefringence
    label: Birefringence (δ)
    value: 0.007
    unit: '-'
    scope: material
    conditions:
      basis: optical value printed for the mineral; wavelength not stated on the page
    method: Infobox value, birefringence row
    status: ground
    source: wiki-ha
    where: Infobox (Identification), Birefringence row
  - benchmark: molar_mass
    label: Formula mass
    value: 502.31
    unit: g/mol
    scope: material
    conditions:
      formula: Ca5(PO4)3OH, as written in the infobox
    method: Infobox value, formula mass row. The infobox formula is the one-half form of the Ca10(PO4)6(OH)2 formula used in the lead.
    status: ground
    source: wiki-ha
    where: Infobox (General), Formula mass row
  - benchmark: hap_mass_fraction_bone
    label: Hydroxyapatite share of bone, by mass
    value: 65
    value_high: 70
    bound: range
    unit: '%'
    scope: material
    conditions:
      basis: bone, by mass, as printed
    method: Biological content sentence in the lead section, printed as 'Bone is 65 to 70% HA by mass'
    status: ground
    source: wiki-ha
    where: Lead section, biological content
  - benchmark: hap_mass_fraction_enamel_dentin
    label: Hydroxyapatite share of dentin and enamel, by mass
    value: 70
    value_high: 80
    bound: range
    unit: '%'
    scope: material
    conditions:
      basis: dentin and enamel, by mass, as printed
    method: Biological content sentence in the lead section, printed as 'dentin and enamel are 70 to 80% HA by mass'
    status: ground
    source: wiki-ha
    where: Lead section, biological content
corrosion:
  - environment: Heating in nitrogen from 30 to 900 °C at 10 °C/min (thermogravimetry)
    headline: The NIST reference powder lost 1.70 % of its mass on heating to 900 °C.
    effect: Total mass loss of 1.70 ± 0.05 % over 30 to 900 °C in nitrogen. The paper reports no decomposition temperature for hydroxyapatite itself. Table 1 separately gives a water mass fraction of 1.59 ± 0.05 %.
    rating: low
    conditions:
      atmosphere: N2
      heating_rate: 10 °C/min
      temperature_range: 30 to 900 °C
    source: markovic2004
    where: Sections 2.3.3 and 3.1.5; Table 1 (H2O row)
  - environment: Saturated solutions at 37.0 °C, equilibrated for 60 days in phosphoric acid
    headline: The solubility product of HA at 37.0 °C is (2.03 ± 0.71) × 10^-59, expanded uncertainty with U = 2uc.
    effect: The paper reports the solubility product only. A very small solubility product indicates low solubility of the solid under these conditions. The paper gives no rating, and no corrosion or dissolution test on coatings or bodies was found.
    rating: low
    conditions:
      temperature: 37.0 ± 0.1 °C
      equilibration: 60 days
      medium: phosphoric acid
    source: markovic2004
    where: Section 3.9
risks:
  hazards:
    - text: PubChem's aggregated GHS record for hydroxylapatite reads 'Not Classified'. It says 'Reported as not meeting GHS hazard criteria by 362 of 370 companies'. Its ECHA notifications summary says 'There are 3 notifications provided by 8 of 370 reports by companies with hazard statement code(s).' The hazard statement codes are not printed on the page read.
      ghs: []
      source: pubchem-ha
      where: Safety and Hazards, 12.1.1 GHS Classification and 12.1.2 Hazard Classes (CID 14781, ECHA C&L summary)
    - text: PubChem's hazards summary, credited to Haz-Map and MSDSonline, reads 'May cause irritation'. This sits alongside the 'Not Classified' GHS record. No supplier safety data sheet was read to settle the difference, so check the supplier's SDS for the grade in use.
      ghs: []
      source: pubchem-ha
      where: Safety and Hazards, 12.1.3 Hazards Summary (CID 14781)
  failure_risks:
    - mode: Mass loss on heating
      trigger: Heating the HA reference powder from 30 to 900 °C in nitrogen at 10 °C/min
      consequence: Total mass loss of 1.70 ± 0.05 % over that range (thermogravimetry)
      severity: low
      source: markovic2004
      where: Sections 2.3.3 and 3.1.5
  side_effects: []
  handling: []
  mitigations: []
uses:
  - application: structures
    device: Bone-graft substitute, and coating for orthopaedic and dental implants
    example: Wikipedia says calcium phosphate ceramics are the preferred bone substitute material in orthopaedic and maxillofacial applications. It also says an HA/polymer composite (HAPEX) is marketed as a plasma-sprayed coating for orthopaedic and dental implants.
    source: wiki-bioceramic
    where: Section 2.1 and Section 8 (commercial usage)
  - application: structures
    device: Dermal filler (calcium hydroxyapatite microspheres, Radiesse)
    example: Wikipedia describes microspheres of 20–45 μm diameter that clear in about 12 to 30 months after injection. The product was FDA approved in 2006.
    source: wiki-ha
    where: Dermal filler (Radiesse) paragraph in the Uses section
supply:
  - subject: Phosphorus (phosphate rock, the source of the phosphate group)
    producers:
      - country: China
        share_percent: 44
        year: 2025
      - country: Morocco
        share_percent: 14.4
        year: 2025
      - country: United States
        share_percent: 8
        year: 2025
      - country: Russia
        share_percent: 5.6
        year: 2025
    critical_lists:
      - list: USGS 2025 List of Critical Minerals (phosphate rock added in the final 2025 list)
        listed: true
    recycling: The USGS phosphate rock chapter gives recycling as None.
    substitutes:
      - 'USGS: there are no substitutes for phosphorus in agriculture. The chapter does not discuss ceramic or biomedical uses.'
    source: usgs-mcs2026-phosphate
    where: World Mine Production table, 2025 (world total 250,000 thousand t; shares calculated by Space Mushroom from the thousand-tonne figures, not printed by USGS); Recycling; Substitutes; introductory text on the final 2025 critical list
documents:
  - title: Preparation and Comprehensive Characterization of a Calcium Hydroxyapatite Reference Material (J. Res. NIST 109, 553-568)
    type: paper
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC4856200/
    year: 2004
  - title: Mineral Commodity Summaries 2026, Phosphate Rock
    type: report
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-phosphate.pdf
    year: 2026
  - title: Hydroxylapatite, PubChem compound record CID 14781
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/14781
    year: 2026
  - title: Resistive coupled microwave sintering - A promising technique to fabricate bioceramics with improved properties
    type: paper
    url: https://pubmed.ncbi.nlm.nih.gov/36201940/
    year: 2022
  - title: Young's Modulus and Vickers Hardness of the Hydroxyapatite Bioceramics with a Small Amount of the Multi-Walled Carbon Nanotubes
    type: paper
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC9369948/
    year: 2022
gaps:
  - No space, vacuum, radiation, thermal-cycling or flight data for HA was found in the sources read. The space use list is empty.
  - Elastic modulus, Vickers hardness, and compressive or flexural strength for dense sintered HA are not recorded in this profile. A 2022 microwave-sintering study (source swapna2022) and a 2022 Materials study (source mat2022) report such values for their own sintered HA, but both describe processes that are not the reference powder's, so neither value is recorded here. The Wikipedia Bioceramic table lists Young's modulus of 73-117 GPa for 'Bioactive HAP' with no form or test stated, so it is not used.
  - 'Density: only specific gravity was read (3.14 to 3.21 measured). The Wikipedia Bioceramic table gives density 3.1 g/cm3 with no form or test, so it is not used.'
  - Melting or decomposition temperature of HA was not found. The melting point in the Wikipedia calcium phosphate infobox belongs to tricalcium phosphate and is not used.
  - Solubility in water or body fluid at pH 7.4 was not found. Only the solubility product is recorded.
  - UNS, EN or AISI designations were not read and are not recorded. The CAS number is recorded from PubChem CID 14781.
  - No supplier safety data sheet was retrieved in this run. The Tosoh, Parchem and Sigma-Aldrich SDS pages tried here did not return a readable HA safety data sheet. The hazards entries come from PubChem's aggregated GHS and hazards-summary data, so the handling and mitigations lists are empty and the side_effects list is empty.
  - Atomic weights were not read in this run, so the recipe parts give atom counts only.
  - Calcium supply and abundance were not read (no USGS calcium data). Only phosphate rock supply is recorded.
  - EU critical raw materials status for phosphate rock was not checked in this run.
  - Ageing in humidity or UV, and thermal expansion of HA, were not found.
  - The Ca/P independent check (1.6649 ± 0.0005) and the stoichiometric Ca/P value stated in the NIST paper are not recorded as properties.
  - The PMC article page (PMC4856200) returned a browser check during this run. The values were read from the Europe PMC full-text copy of the same article, so the source URL may not verify automatically.
  - The NIST SRM 2910 certificate PDF did not download in this run (the server returned an HTML page), so no certified values beyond Table 1 and Table 6 of the paper are used.
  - The application list has no medical or dental category. Both medical uses are filed under 'structures' as the nearest option. No space application was found.
  - The brief proposes a new 'Bioceramics' type. This file uses the existing bio-grown-building-materials type, and taxonomy was not changed.
  - No image (media) was read or licensed in this run.
sources:
  markovic2004:
    title: Preparation and Comprehensive Characterization of a Calcium Hydroxyapatite Reference Material
    id: doi:10.6028/jres.109.042 (J. Res. NIST 109, 553-568; PMC4856200)
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC4856200/
    year: 2004
    kind: paper
    license: not read in this run
  wiki-ha:
    title: Hydroxyapatite (Wikipedia article)
    id: en.wikipedia.org, read 2026-11-01
    url: https://en.wikipedia.org/wiki/Hydroxyapatite
    year: 2026
    kind: web
    license: CC BY-SA 4.0 (Wikipedia text)
  wiki-bioceramic:
    title: Bioceramic (Wikipedia article)
    id: en.wikipedia.org, read 2026-11-01
    url: https://en.wikipedia.org/wiki/Bioceramic
    year: 2026
    kind: web
    license: CC BY-SA 4.0 (Wikipedia text)
  usgs-mcs2026-phosphate:
    title: Mineral Commodity Summaries 2026, Phosphate Rock
    id: USGS MCS 2026, February 2026
    url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-phosphate.pdf
    year: 2026
    kind: report
    license: public domain (USGS)
  nist-srm-shop:
    title: NIST SRM Online Request System redirect page (SRM ordering moved to the NIST shop)
    id: shop.nist.gov, page pageKey=SRMORS, read 2026-11-01
    url: https://shop.nist.gov/ccrz__CCPage?pageKey=SRMORS
    year: 2026
    kind: web
    license: not read in this run
  pubchem-ha:
    title: Hydroxylapatite (Ca5(OH)(PO4)3), PubChem compound record CID 14781
    id: PubChem CID 14781, CAS 1306-06-5, read 2026-11-01
    url: https://pubchem.ncbi.nlm.nih.gov/compound/14781
    year: 2026
    kind: database
    license: PubChem public record; ECHA data as cited by PubChem under the ECHA legal notice
  swapna2022:
    title: Resistive coupled microwave sintering - A promising technique to fabricate bioceramics with improved properties
    id: doi:10.1016/j.jmbbm.2022.105488 (J Mech Behav Biomed Mater, 2022; PubMed 36201940)
    url: https://pubmed.ncbi.nlm.nih.gov/36201940/
    year: 2022
    kind: paper
    license: not read in this run
  mat2022:
    title: Young's Modulus and Vickers Hardness of the Hydroxyapatite Bioceramics with a Small Amount of the Multi-Walled Carbon Nanotubes
    id: doi:10.3390/ma15155304 (Materials, 2022; PMC9369948)
    url: https://pmc.ncbi.nlm.nih.gov/articles/PMC9369948/
    year: 2022
    kind: paper
    license: not read in this run
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 20
  unreachable: 2
  caveats: 3
  note: Read by an AI assistant on 2026-11-01. Values taken from NIST paper Tables 1 and 6 and Sections 3.1.3, 3.2, 3.9 and 2.3.3 (via the Europe PMC full-text copy) and from the Wikipedia infobox for HA. PMC and PubChem pages returned browser checks; the SRM certificate PDF did not download. Hazard data come from PubChem's GHS record. Modulus data are not recorded in this profile.
story:
  recipe:
    line: Hydroxyapatite is a calcium phosphate with the formula Ca10(PO4)6(OH)2. Each formula unit joins ten calcium ions, six phosphate groups (PO4) and two hydroxide groups (OH). The synthesis equation printed on Wikipedia is 10 Ca(OH)2 + 6 H3PO4 → Ca10(PO4)6(OH)2 + 18 H2O.
    parts:
      - name: Calcium
        symbol: Ca
        role: The ion that sets the Ca/P ratio. The reference powder has 39.15 % calcium by mass (Table 1).
      - name: Phosphorus
        symbol: P
        role: Sits at the centre of each phosphate group. Phosphate makes up 55.16 % of the reference powder by mass (Table 1).
      - name: Oxygen
        symbol: O
        role: Oxygen atoms of the phosphate and hydroxide groups. Atomic weight not read in this run.
      - name: Hydrogen
        symbol: H
        role: Hydrogen of the hydroxide groups. Water is 1.59 % of the reference powder by mass (Table 1).
  risk_groups:
    - title: For people
      level: 0
      verdict: Not GHS-classified in PubChem; irritation noted
      lead: PubChem's aggregated GHS record lists hydroxyapatite as Not Classified, and its hazards summary reads May cause irritation. No supplier safety data sheet was read in this run.
      points:
        - label: Dust
          line: Dust exposure was not assessed in the sources read. Check the supplier's safety data sheet before handling the powder.
    - title: If the material is heated
      lead: The heating data here are thermogravimetry results on a reference powder, not incident reports.
      points:
        - label: Mass loss
          line: On heating from 30 to 900 °C in nitrogen at 10 °C/min, the NIST reference powder lost 1.70 ± 0.05 % of its mass.
    - title: Handling and storage
      points:
        - label: Source gap
          line: The sources read here give no storage or handling instructions for HA powder.
  why: Hydroxyapatite (HA, Ca10(PO4)6(OH)2) is the calcium phosphate mineral of bone. Wikipedia gives bone as 65 to 70 % HA by mass and dentin and enamel as 70 to 80 % HA by mass. NIST characterised a calcium hydroxyapatite reference powder, SRM 2910, and reports its composition, unit cell, surface area and thermal behaviour (Markovic et al., 2004). NIST now orders its Standard Reference Materials through its shop at shop.nist.gov.
  uses:
    - where: Bone substitutes and implant coatings
      line: Wikipedia says calcium phosphate ceramics are the preferred bone substitute material in orthopaedic and maxillofacial applications. It also says an HA/polymer composite (HAPEX) is marketed as a plasma-sprayed coating for orthopaedic and dental implants.
    - where: Dermal filler
      line: Wikipedia describes a calcium hydroxyapatite dermal filler (Radiesse) with microspheres of 20 to 45 μm diameter. The microspheres clear in about 12 to 30 months, and the product was FDA approved in 2006.
  can_do:
    - label: Calcium-to-phosphorus ratio
      benchmark: ca_p_molar_ratio
      value: 1.664 ± 0.005
      line: The NIST reference powder has a Ca/P molar ratio of 1.664 ± 0.005, close to the ratio the formula Ca10(PO4)6(OH)2 requires.
    - label: Crystal lattice
      benchmark: lattice_parameter_a
      value: a = 0.94238 nm, c = 0.68854 nm
      line: The reference powder is hexagonal, with a = 0.94238 ± 0.00009 nm and c = 0.68854 ± 0.00006 nm (Table 6, Standard row).
    - label: Surface area
      benchmark: bet_surface_area
      value: 18.3 m2/g
      line: The BET surface area of the precipitated reference powder is 18.3 ± 0.3 m2/g, from the mean of 12 samples. Individual samples ranged from 17.7 to 19.1 m2/g.
    - label: Solubility
      benchmark: solubility_product
      value: (2.03 ± 0.71) × 10^-59
      line: At 37.0 °C the solubility product of HA is (2.03 ± 0.71) × 10^-59, an expanded uncertainty. Dissolution rates in body fluid were not found.
    - label: Heating
      benchmark: thermal_mass_loss
      value: 1.70 %
      line: Heated from 30 to 900 °C in nitrogen, the powder lost 1.70 ± 0.05 % of its mass. The paper gives no decomposition temperature for HA itself.
    - label: Specific gravity
      benchmark: specific_gravity
      value: 3.14 to 3.21
      line: Measured specific gravity is 3.14 to 3.21, and the calculated value is 3.16 (Wikipedia infobox). Specific gravity is the ratio of density to the density of water, so it has no unit.
    - label: Hardness
      benchmark: mohs_hardness
      value: '5'
      line: Mohs hardness is 5 (Wikipedia infobox). No Vickers hardness, elastic modulus or strength value for dense HA is recorded in this profile.
  compare: Hydroxyapatite is the calcium phosphate that bone and enamel are built from. In the sources read, its reference powder sits very close to the stoichiometric Ca/P ratio, which is why the composition is well defined. The sources read give no like-for-like mechanical comparison with other bioceramics, so this profile makes no ranking on strength or stiffness.
  compare_rows:
    - label: Ca/P molar ratio
      benchmark: ca_p_molar_ratio
    - label: Surface area (BET)
      benchmark: bet_surface_area
    - label: Mohs hardness
      benchmark: mohs_hardness
  handling:
    - No supplier safety data sheet or handling instruction for HA powder was read in this run.
    - Check the supplier's data sheet for dust and storage advice before use.
  good_for:
    - 'Calcium phosphate composition work: the NIST reference powder has a Ca/P ratio of 1.664 ± 0.005 and documented unit-cell parameters.'
    - 'Bone-substitute and implant-coating context: Wikipedia describes calcium phosphate ceramics as the preferred bone substitute in orthopaedic and maxillofacial applications.'
  watch_out:
    - No modulus, hardness or strength value for dense sintered HA is recorded in this profile.
    - The surface area and crystal size given here describe the precipitated reference powder, not a sintered body.
    - The Wikipedia calcium phosphate infobox values belong to tricalcium phosphate, a different compound, and are not used here.
  verdict: Hydroxyapatite has documented composition, unit-cell and surface-area data from NIST. Its mechanical data are missing from this record, so no structural ranking is made.