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Collophane

Apatite group
Apatite Canada.jpg
General
Category Phosphate mineral
Formula
(repeating unit)
Ca5(PO4)3(F,Cl,OH)
Strunz classification 8.BN.05
Crystal system Hexagonal
Crystal class Dipyramidal (6/m)
(same H-M symbol)
Identification
Color Transparent to translucent, usually green, less often colorless, yellow, blue to violet, pink, brown.
Crystal habit Tabular, prismatic crystals, massive, compact or granular
Cleavage [0001] indistinct, [1010] indistinct
Fracture Conchoidal to uneven
Mohs scale hardness 5 (defining mineral)
Luster Vitreous to subresinous
Streak White
Diaphaneity Transparent to translucent
Specific gravity 3.16–3.22
Polish luster Vitreous
Optical properties Double refractive, uniaxial negative
Refractive index 1.634–1.638 (+0.012, −0.006)
Birefringence 0.002–0.008
Pleochroism Blue stones – strong, blue and yellow to colorless. Other colors are weak to very weak.
Dispersion 0.013
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.

Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite and chlorapatite, with high concentrations of OH, F and Clions, respectively, in the crystal. The formula of the admixture of the four most common endmembers is written as Ca10(PO4)6(OH,F,Cl)2, and the crystal unit cell formulae of the individual minerals are written as Ca10(PO4)6(OH)2, Ca10(PO4)6(F)2 and Ca10(PO4)6(Cl)2.

The mineral was named apatite by the German geologist Abraham Gottlob Werner in 1786, although the specific mineral he had described was reclassified as fluorapatite in 1860 by the German mineralogist Karl Friedrich August Rammelsberg. Apatite is a mineral that is often mistaken for other minerals. This tendency is reflected in the mineral's name, which is derived from the Greek word απατείν (apatein), which means to deceive or to be misleading.

Apatite is one of a few minerals produced and used by biological micro-environmental systems. Apatite is the defining mineral for 5 on the Mohs scale. Hydroxyapatite, also known as hydroxylapatite, is the major component of tooth enamel and bone mineral. A relatively rare form of apatite in which most of the OH groups are absent and containing many carbonate and acid phosphate substitutions is a large component of bone material.


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Wikipedia

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