Hydroxyapatite

Hydroxyapatite
Hydroxyapatite
	Hydroxyapatite crystals on matrix
General
Category	Phosphate mineral ; Apatite group
Formula; (repeating unit)	Ca5(PO4)3OH
IMA symbol	Hap
Strunz classification	8.BN.05
Crystal system	Hexagonal
Crystal class	Dipyramidal (6/m) ; H-M symbol (6/m)
Space group	P63/m
Unit cell	a = 9.41 Å, c = 6.88 Å; Z = 2
Identification
Formula mass	502.31 g/mol
Color	Colorless, white, gray, yellow, yellowish green
Crystal habit	As tabular crystals and as stalagmites, nodules, in crystalline to massive crusts
Cleavage	Poor on {0001} and {1010}
Fracture	Conchoidal
Tenacity	Brittle
Mohs scale hardness	5
Luster	Vitreous to subresinous, earthy
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	3.14–3.21 (measured), 3.16 (calculated)
Optical properties	Uniaxial (−)
Refractive index	nω = 1.651 nε = 1.644
Birefringence	δ = 0.007
References

A 3D visualization of half of a hydroxyapatite unit cell, from x-ray crystallography

Hydroxyapatite (IMA name: hydroxylapatite^[5]) (Hap, HAp, or HA) is a naturally occurring mineral form of calcium apatite with the formula Ca₅(PO₄)₃(OH), often written Ca₁₀(PO₄)₆(OH)₂ to denote that the crystal unit cell comprises two entities.^[6] It is the hydroxyl endmember of the complex apatite group. The OH⁻ ion can be replaced by fluoride or chloride, producing fluorapatite or chlorapatite. It crystallizes in the hexagonal crystal system. Pure hydroxyapatite powder is white. Naturally occurring apatites can, however, also have brown, yellow, or green colorations, comparable to the discolorations of dental fluorosis.

Up to 50% by volume and 70% by weight of human bone is a modified form of hydroxyapatite, known as bone mineral.^[7] Carbonated calcium-deficient hydroxyapatite is the main mineral of which dental enamel and dentin are composed. Hydroxyapatite crystals are also found in pathological calcifications such as those found in breast tumors,^[8] as well as calcifications within the pineal gland (and other structures of the brain) known as corpora arenacea or "brain sand".^[9]

^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
^ Hydroxylapatite on Mindat
^ Hydroxylapatite on Webmineral
^ Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (2000). "Hydroxylapatite". Handbook of Mineralogy (PDF). Vol. IV (Arsenates, Phosphates, Vanadates). Chantilly, VA, US: Mineralogical Society of America. ISBN 978-0962209734. Archived (PDF) from the original on 2018-09-29. Retrieved 2010-08-29.
^ "The official IMA-CNMNC List of Mineral Names". International Mineralogical Association: COMMISSION ON NEW MINERALS, NOMENCLATURE AND CLASSIFICATION. Retrieved 24 August 2023.
^ Singh, Anamika; Tiwari, Atul; Bajpai, Jaya; Bajpai, Anil K. (2018-01-01), Tiwari, Atul (ed.), "3 – Polymer-Based Antimicrobial Coatings as Potential Biomaterials: From Action to Application", Handbook of Antimicrobial Coatings, Elsevier, pp. 27–61, doi:10.1016/b978-0-12-811982-2.00003-2, ISBN 978-0-12-811982-2, retrieved 2020-11-18
^ Junqueira, Luiz Carlos; José Carneiro (2003). Foltin, Janet; Lebowitz, Harriet; Boyle, Peter J. (eds.). Basic Histology, Text & Atlas (10th ed.). McGraw-Hill Companies. p. 144. ISBN 978-0-07-137829-1. Inorganic matter represents about 50% of the dry weight of bone ... crystals show imperfections and are not identical to the hydroxylapatite found in the rock minerals
^ Haka, Abigail S.; Shafer-Peltier, Karen E.; Fitzmaurice, Maryann; Crowe, Joseph; Dasari, Ramachandra R.; Feld, Michael S. (2002-09-15). "Identifying microcalcifications in benign and malignant breast lesions by probing differences in their chemical composition using Raman spectroscopy". Cancer Research. 62 (18): 5375–5380. ISSN 0008-5472. PMID 12235010.
^ Angervall, Lennart; Berger, Sven; Röckert, Hans (2009). "A Microradiographic and X-Ray Crystallographic Study of Calcium in the Pineal Body and in Intracranial Tumours". Acta Pathologica et Microbiologica Scandinavica. 44 (2): 113–19. doi:10.1111/j.1699-0463.1958.tb01060.x. PMID 13594470.

[1] Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.

[2] Hydroxylapatite on Mindat

[3] Hydroxylapatite on Webmineral

[HB-4] Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C., eds. (2000). "Hydroxylapatite". Handbook of Mineralogy (PDF). Vol. IV (Arsenates, Phosphates, Vanadates). Chantilly, VA, US: Mineralogical Society of America. ISBN 978-0962209734. Archived (PDF) from the original on 2018-09-29. Retrieved 2010-08-29.

[IMA_names-5] "The official IMA-CNMNC List of Mineral Names". International Mineralogical Association: COMMISSION ON NEW MINERALS, NOMENCLATURE AND CLASSIFICATION. Retrieved 24 August 2023.

[6] Singh, Anamika; Tiwari, Atul; Bajpai, Jaya; Bajpai, Anil K. (2018-01-01), Tiwari, Atul (ed.), "3 – Polymer-Based Antimicrobial Coatings as Potential Biomaterials: From Action to Application", Handbook of Antimicrobial Coatings, Elsevier, pp. 27–61, doi:10.1016/b978-0-12-811982-2.00003-2, ISBN 978-0-12-811982-2, retrieved 2020-11-18

[7] Junqueira, Luiz Carlos; José Carneiro (2003). Foltin, Janet; Lebowitz, Harriet; Boyle, Peter J. (eds.). Basic Histology, Text & Atlas (10th ed.). McGraw-Hill Companies. p. 144. ISBN 978-0-07-137829-1. Inorganic matter represents about 50% of the dry weight of bone ... crystals show imperfections and are not identical to the hydroxylapatite found in the rock minerals

[8] Haka, Abigail S.; Shafer-Peltier, Karen E.; Fitzmaurice, Maryann; Crowe, Joseph; Dasari, Ramachandra R.; Feld, Michael S. (2002-09-15). "Identifying microcalcifications in benign and malignant breast lesions by probing differences in their chemical composition using Raman spectroscopy". Cancer Research. 62 (18): 5375–5380. ISSN 0008-5472. PMID 12235010.

[9] Angervall, Lennart; Berger, Sven; Röckert, Hans (2009). "A Microradiographic and X-Ray Crystallographic Study of Calcium in the Pineal Body and in Intracranial Tumours". Acta Pathologica et Microbiologica Scandinavica. 44 (2): 113–19. doi:10.1111/j.1699-0463.1958.tb01060.x. PMID 13594470.

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