Apatite

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Apatite
Apatite crystals.jpg
General
Category Phosphate mineral group
Chemical formula Ca5(PO4)3(F,Cl,OH)
Identification
Color Transparent to translucent, usually green, less often colorless, yellow, blue to violet, pink, brown.[1]
Crystal habit Tabular, prismatic crystals, massive, compact or granular
Crystal system Hexagonal dipyramidal (6/m)[2]
Cleavage [0001] indistinct, [1010] indistinct[2]
Fracture Conchoidal to uneven[1]
Mohs Scale hardness 5[1] (defining mineral)
Luster Vitreous[1] to subresinous
Polish luster Vitreous[1]
Refractive index 1.634–1.638 (+0.012, −0.006)[1]
Optical Properties Double refractive, uniaxial negative[1]
Birefringence 0.002–0.008[1]
Dispersion 0.013[1]
Pleochroism Blue stones – strong, blue and yellow to colorless. Other colors are weak to very weak.[1]
Ultraviolet fluorescence Yellow stones – purplish pink which is stronger in long wave; blue stones – blue to light blue in both long and short wave; green stones – greenish yellow which is stronger in long wave; violet stones – greenish yellow in long wave, light purple in short wave.[1]
Streak White
Specific gravity 3.16–3.22[2]
Diaphaneity Transparent to translucent[2]

Apatite is a group of phosphate minerals with high concentrations of OH, F, Cl or ions, respectively, in the crystal.

Apatite is characteristic of biological systems. It is one of a few minerals produced and used by biological micro-environmental systems. It hardness defines 5 on the Mohs scale. Hydroxyapatite is the main component of tooth enamel and bone mineral.

Much bone material is in a relatively rare form of apatite. In this form most of the OH groups are absent, and there are many carbonate and acid phosphate substitutions.

Fluorapatite (or fluoroapatite) is more resistant to acid attack than is hydroxyapatite. In the mid-20th century it was discovered that communities whose water supply naturally contained fluorine had lower rates of dental caries.[3] Fluoridated water allows exchange in the teeth of fluoride ions for hydroxyl groups in apatite. Similarly, toothpaste often includes a source of fluoride anions (e.g. sodium fluoride, sodium monofluorophosphate).

References[change | change source]

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
  2. 2.0 2.1 2.2 2.3 Apatite. Webmineral
  3. National Institute of Dental and Craniofacial Research. The story of fluoridation; 2008-12-20.