From Encyclopedia Jr, free information reference for Kids
| Apatite |
 |
| General |
| Category |
Mineral |
| Chemical formula |
Ca5(PO4)3(F,Cl,OH) |
| Identification |
| Color |
Usually green, less often colorless, yellow, blue to violet. |
| Crystal habit |
Tabular, prismatic crystals, massive, compact or granular. |
| Crystal system |
Hexagonal |
| Cleavage |
Poor |
| Fracture |
Conchoidal to even |
| Mohs Scale hardness |
5 |
| Luster |
Vitreous to subresinous |
| Refractive index |
1.632-1.646. Biref .002-.004 |
| Pleochroism |
None |
| Streak |
White |
| Specific gravity |
3.17-3.23 |
| Major varieties |
| None |
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, and a large component of bone material.
Fluorapatite (or fluoroapatite) is slightly stronger than hydroxyapatite; thus, fluoridated water, which will allow exchange in the teeth of hydroxyl ions for fluoride ions, slightly strengthens the teeth, although too much results in dental fluorosis and/or skeletal fluorosis. Fluorapatite is also far more resistant to acid attack and therefore a major constituent of toothpaste is a source of fluoride anions (e.g. sodium fluoride, sodium monofluorophosphate).
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.
[edit] See also
- List of minerals
- Thermal history modelling
[edit] Further reading
- Schmittner Karl-Erich and Giresse Pierre, 1999. Micro-environmental controls on biomineralization: superficial processes of apatite and calcite precipitation in Quaternary soils, Roussillon, France. Sedimentology 46/3: 463-476.
[edit] External links
