Apatite
<<Check Amethyst Galleries for a broader definition of the Apatite group of minerals.>>
| Apatite | |
|---|---|
 |
|
| 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] |
| Luster | Vitreous[1] to subresinous |
| Refractive index | 1.634 - 1.638 (+.012, -.006)[1] |
| Optical Properties | Double refractive, uniaxial negative[1] |
| Birefringence | .002-.008[1] |
| Pleochroism | Blue stones - strong, blue and yellow to colorless. Other colors are weak to very weak.[1] |
| Streak | White |
| Specific gravity | 3.16 - 3.22[2] |
| Diaphaneity | Transparent to translucent[2] |
Apatite is a group of phosphate minerals, usually referring to hydroxylapatite, fluorapatite, and chlorapatite, named for high concentrations of OH-, F-, or Cl- ions, respectively, in the crystal. The formula of the admixture of the three most common species is written as Ca5(PO4)3(OH, F, Cl), and the formulae of the individual minerals are written as Ca5(PO4)3(OH), Ca5(PO4)3F and Ca5(PO4)3Cl, respectively.
Apatite is one of few minerals that are produced and used by biological micro-environmental systems. Hydroxylapatite is the major component of tooth enamel. A relatively unique 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.
Fluorapatite (or fluoroapatite) is more resistant to acid attack that is hydroxyapatite. For this reason, toothpaste typically contain a source of fluoride anions (e.g. sodium fluoride, sodium monofluorophosphate). Similarly, fluoridated water, allow exchange in the teeth of fluoride ions for hydroxy groups in apatite. Too much fluoride results in dental fluorosis and/or skeletal fluorosis.
In the United States, apatite is often used to fertilize tobacco. It partially starves the plant of nitrogen, which gives American cigarettes a different taste from those of other countries.
Fission tracks in apatite are commonly used to determine the thermal history of orogenic (mountain) belts and of sediments in sedimentary basins.
Phosphorite is the name given to impure, massive apatite.
Fluoroapatite
| Fluoroapatite | |
|---|---|
| |
| General | |
| Systematic name | Fluoroapatite |
| Other names | Fluorapatite |
| Molecular formula | Ca5(PO4)3F |
| Molar mass | 504.3 g/mol |
| Appearance | hard solid, various colors |
| CAS number | 68877-08-7 |
| Properties | |
| Solubility in water | almost insoluble |
| Structure | |
| Crystal structure | hexagonal |
| Related compounds | |
| Related compounds | Ca5(PO4)3OH Ca5(PO4)3Cl |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references | |
Fluoroapatite, often with the alternate spelling of fluorapatite, is a mineral with the formula Ca5(PO4)3F (calcium halophosphate). Fluoroapatite is a hard crystalline solid. Although samples can have various color (green, brown, blue, violet, or colorless), the pure mineral is colorless as expected for a material lacking transition metals. It is an important constituent of tooth enamel.[3]
Fluoroapatite crystallizes in a hexagonal crystal system. It is often combined as a solid solution with hydroxylapatite (Ca5(PO4)3OH) in biological matrices. Chloroapatite (Ca5(PO4)3Cl) is another related structure.[3]
Fluoroapatite can be synthesized in a two step process. First, calcium phosphate is generated by combining calcium and phosphate salts at neutral pH.This material then reacts further with fluoride sources (often sodium monofluorophosphate or calcium fluoride (CaF2)) to give the mineral. This reaction is integral in the global phosphorous cycle.[4]
- 3Ca2+ + 2PO43- → Ca3(PO4)2
- 3 Ca3(PO4)2 + CaF2 → 2 Ca5(PO4)3F
Fluoroapatite can also be used as a precursor for the production of phosphorus. The mineral can be reduced by carbon in the presence of quartz, ultimately generating white phosphorus, P4:
- Ca5(PO4)3F + 3SiO2 + 5C → 3CaSiO3 + 5CO + P2
2P2 → P4 after cooling
Gemology
Apatite is infrequently used as a gemstone. Transparent stones of clean color have been faceted, and chatoyant specimens have been cabochon cut.[1] Chatoyant stones are known as cat's-eye apatite,[1] transparent green stones are known as asparagus stone,[1] and blue stones have been called moroxite.[5] Crystals of rutile may have grown in the crystal of apatite so when in the right light, the cut stone displays a cat's eye effect. Major sources for gem apatite are:[1] Brazil, Burma, and Mexico. Other sources include:[1] Canada, Czechoslovakia, Germany, India, Madagascar, Mozambique, Norway, South Africa, Spain, Sri Lanka, and the United States.
See also
Notes
- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
- ↑ 2.0 2.1 2.2 2.3 Apatite Mineral Data. Webmineral.com. Retrieved May 8, 2007.
- ↑ 3.0 3.1 Hurlbert and Klein. "Manual of Mineralogy, 19th Edition." 1977. ISBN 0471251771.
- ↑ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
- ↑ Streeter, Edwin W., Moroxite Precious Stones and Gems 6th ed., George Bell and Sons, London, 1898, p306. Retrieved May 8, 2007.
ReferencesISBN links support NWE through referral fees
- Farndon, John. 2006. The Practical Encyclopedia of Rocks & Minerals: How to Find, Identify, Collect and Maintain the World's best Specimens, with over 1000 Photographs and Artworks. London: Lorenz Books. ISBN 0754815412.
- Klein, Cornelis, and Barbara Dutrow. 2007. Manual of Mineral Science. 23rd ed. New York: John Wiley. ISBN 978-0471721574.
- Pellant, Chris. 2002. Rocks and Minerals. Smithsonian Handbooks. New York: Dorling Kindersley. ISBN 0789491060.
- Shaffer, Paul R., Herbert S. Zim, and Raymond Perlman. 2001. Rocks, Gems and Minerals. Rev. ed. New York: St. Martin's Press. ISBN 1582381321.
- Mineral Gallery. 2006. The Mineral Apatite. Amethyst Galleries. Retrieved May 8, 2007.
- Mineral Gallery. 2006. The Apatite Group of Minerals. Amethyst Galleries. Retrieved May 8, 2007.
External links
- Apatite. Mindat.org. Retrieved May 8, 2007.
- Apatite Group. Mindat.org. Retrieved May 8, 2007.
- Apatite Mineral Data. Webmineral.com. Retrieved May 8, 2007.
- Fluoroapatite. Webmineral.com. Retrieved May 8, 2007.
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