apatite(redirected from Asparagus-stone)
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apatite(ăp`ətīt), mineral, a phosphate of calcium containing chlorine or fluorine, or both, that is transparent to opaque in shades of green, brown, yellow, white, red, and purple. Apatite is a minor constituent in igneous and metamorphic rocks. Yellow-green asparagus stone and blue-green manganapatite are used in jewelry. Apatite is mined to make phosphatic fertilizers and is used in fission track dating of rocks (see datingdating,
the determination of the age of an object, of a natural phenomenon, or of a series of events. There are two basic types of dating methods, relative and absolute.
..... Click the link for more information. ). Commercial deposits are mined in Idaho, Tennessee, and Wyoming, and in N Africa and Russia.
a mineral of the calcium phosphate group containing a variable quantity of fluorine and chlorine. The chemical formula of apatite is 3Ca3 (PO4) 2·Ca(F, Cl)2. As secondary admixtures apatite sometimes contains up to 10 percent oxides of manganese, strontium, or rare earth elements; less than 1 percent sodium, potassium, or barium frequently replaces part of the calcium. In addition to F- and Cl-, (OH)-, O2-, and CO32-, are also present. Fluor-, chlor-, hydroxyl-, carbonate-, and oxy-apatite have been isolated, as have been manganapatite, strontium apatite, and rare earth apatite (“belovit”). The theoretical composition P2O5 in fluorapatite and chlorapatite is 42.3 percent and 41.1 percent respectively. Apatite crystallizes in a hexagonal system. Crystals are for the most part hexahedral, prismatic, and elongated to the point of being needlelike; they are rarely tabular. Apatite is also found in the form of cryptocrystalline varieties (col-lophanite). The color and other physical and optical properties change within the bounds of the series of fluor-, chlor-, and hydroxylapatite as well as according to the composition of the admixtures of elements. The green color of apatite is caused by the presence of iron, its blue color by manganese, and its brown and red color by a finely dispersed admixture of hematite. Its cleavage is incomplete; its luster is vitreous and resinous; its hardness on the mineralogical scale is 5; and its density ranges from 3,160 to 3,200 kg/m3 but reaches 3,800–4,200 kg/m3 in varieties enriched with strontium and the rare earths. The melting point is 1660°C for fluorapatite and 1530°C for chlorapatite.
Apatite is widely distributed in rocks and is formed by various geological processes. Large apatite ore accumulations are confined to massive alkaline rocks (nepheline syenites). A high apatite content has also been established in carbonatites and in certain iron ore deposits formed at high temperatures. In addition, apatite is found in granite, pegmatites, quartz veins, crystalline schists. In sedimentary rocks, minerals of the apatite group occur mainly in the form of phosphorites and partly in excavated bones. Because of its relative chemical stability, apatite is found in placers.
Most of the apatite which is mined is utilized in the manufacture of phosphorous fertilizers. In the chemical industry apatite yields phosphoric acid, various salts, phosphorus, and phosphorous compounds. Apatite is also used in ferrous and nonferrous metallurgy and in the ceramic and glass industries.
The world’s largest deposit of apatite is found in the USSR on the Kola Peninsula. Abroad, the largest deposits of apatite are found in the iron ore fields of Sweden (Kierunavaara, Luossavaara) and in the carbonatóte fields of central and eastern Africa.
REFERENCESBok, I. I. Agronomicheskie rudy, 2nd ed. Alma-Ata, 1965.
Deer, W. A., R. A. Howie, and J. Zussman. Porodoobrazuiushchie mineraly, vol. 5. Moscow, 1966. (Translated from English.)
A. M. PORTNOV