RockHoundBlog

Apatite- Minerals of the day

Filed under: Mineral of the day,regular postings — Gary January 31, 2007 @ 2:00 am

Apatite_crystals Apatite_crystals_2

Apatite_crystals_with_dolmiteApatite_crystals_with_dolmite

Apatite_with_MuscoviteApatite_with_Muscovite

“Apatite is infrequently used as a gemstone. Transparent stones of clean color have been faceted, and chatoyant specimens have been cabochon cut.”

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 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.

Gemology

Apatite is infrequently used as a gemstone. Transparent stones of clean color have been faceted, and chatoyant specimens have been cabochon cut. Chatoyant stones are known as cat’s-eye apatite,

In gemology, chatoyancy (or chatoyance) is an optical reflectance effect seen in certain gemstones. Coined from the French, meaning “cat’s eye,” chatoyancy arises either from the fibrous structure of a material, as in tiger eye quartz, or from fibrous inclusions or cavities within the stone, as in cat’s eye chrysoberyl. The effect can be likened to the sheen off a spool of silk; the mobile, wavering reflection always being perpendicular to the direction of the fibres. For a gemstone to show this effect it must be cut en cabochon, with the fibers or fibrous structures parallel to the base of the finished stone.

Some gem species known for this phenomenon include the aforementioned quartz, chrysoberyl, beryl (especially var. aquamarine), tourmaline, apatite, and scapolite.

Chatoyancy can also be used to refer to a similar effect in woodworking, where certain finishes will cause the wood grain to achieve a striking three-dimensional appearance.

tigers-eye

transparent green stones are known as asparagus stone, and blue stones have been called moroxite. Major sources for gem apatite are: Brazil, Burma, and Mexico. Other sources include: Canada, Czechoslovakia, Germany, India, Madagascar, Mozambique, Norway, South Africa, Spain, Sri Lanka, and the US.

No Comments »

No comments yet.

RSS feed for comments on this post. TrackBack URI

Leave a comment

You must be logged in to post a comment.