Apatite

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Apatite group
Apatite09.jpg
General
CategoryPhosphate mineral
Formula
(repeating unit)
Ca5(PO4)3(F,Cl,OH)
Strunz classification08.BN.05
Identification
ColorTransparent to translucent, usually green, less often colorless, yellow, blue to violet, pink, brown.[1]
Crystal habitTabular, prismatic crystals, massive, compact or granular
Crystal systemHexagonal dipyramidal (6/m)[2]
Cleavage[0001] indistinct, [1010] indistinct[2]
FractureConchoidal to uneven[1]
Mohs scale hardness5[1] (defining mineral)
LusterVitreous[1] to subresinous
StreakWhite
DiaphaneityTransparent to translucent[2]
Specific gravity3.16–3.22[2]
Polish lusterVitreous[1]
Optical propertiesDouble refractive, uniaxial negative[1]
Refractive index1.634–1.638 (+0.012, −0.006)[1]
Birefringence0.002–0.008[1]
PleochroismBlue stones – strong, blue and yellow to colorless. Other colors are weak to very weak.[1]
Dispersion0.013[1]
Ultraviolet fluorescenceYellow 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]

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.