Hydroxylapatite is a naturally occurring form of calcium apatite with the formula Ca₅(PO₄)₃(OH), but is usually written Ca₁₀(PO₄)₆(OH)₂ to denote that the crystal unit cell comprises two molecules. Hydroxylapatite is the hydroxyl endmember of the complex apatite group. The OH^- ion can be replaced by fluoride, chloride or carbonate. It crystallizes in the hexagonal (crystal system) crystal system It has a specific gravity of 3.08 and is 5 on the Mohs hardness scale. Pure hydroxylapatite powder is white. Naturally occurring apatites can however also have brown, yellow or green colorations. Compare to the discolorations of dental fluorosis. Apatite is a group of minerals, usually referring to: hydroxylapatite, fluorapatite, and chlorapatite, named for high concentrations of OH-, F-, or Cl- ions, respectively, in the crystal lattice. ... Hydroxide is a functional group consisting of oxygen and hydrogen: -O−H It has a charge of 1-. The term hydroxyl group is used when the functional group -OH is counted as a substituent of an organic compound. ... An ion is an elementary particle or system of elementary particles with a net electric charge. ... General Name, Symbol, Number fluorine, F, 9 Chemical series halogens Group, Period, Block 17, 2, p Appearance pale greenish-yellow gas Atomic mass 18. ... General Name, Symbol, Number chlorine, Cl, 17 Chemical series halogens Group, Period, Block 17, 3, p Appearance yellowish green Atomic mass 35. ... Carbonate is an anion with a charge of -2 and an empirical formula of CO32-. An aqueous solution of carbon dioxide contains a minute amount of H2CO3, called carbonic acid, which dissociates to form hydrogen ions and carbonate ions. ... In crystallography, the hexagonal crystal system is one of the 7 lattice point groups. ... In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... Relative density (also known as specific gravity) is a measure of the density of a material. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... Dental fluorosis occurs during tooth development especially between the ages of 6 months to 5 years, from the overexposure to fluoride. ...

The name apatite derives from a Greek apatao - "I am misleading" in allusion to its confusion with similar appearing gemstones. A gemstone is a mineral, rock (as in lapis lazuli) or petrified material that when cut or faceted and polished is collectible or can be used in jewellery. ...

Medical uses

Hydroxylapatite can be used as a filler to replace amputated bone or as a coating to promote bone ingrowth into prosthetic implants. Although many other phases exist with similar or even identical chemical makeup, the body responds much differently to them. Coral skeletons can be transformed into hydroxylapatite by high temperatures; their porous structure allows relatively rapid ingrowth at the expense of initial mechanical strength. The high temperature also burns away any organic molecules such as proteins, preventing host vs. graft disease. A United States soldier demonstrates Foosball with two prosthetic limbs In medicine, a prosthesis is an artificial extension that replaces a missing part of the body. ... In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... Orders see Anthozoa A coral reef can be an oasis of marine life. ... A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... Transplant rejection is a process by which the immune system of the recipient of a transplant attacks the transplanted organ or tissue. ...

External links

• Material overview
• International Mineralogical Association
• HA on webmineral.com
• HA om mindat.org

Reference

• Wopenka, B. and J.D. Pasteris, A mineralogical perspective on the apatite in bone. Materials Science and Engineering: C. 25(2): 131, 2005