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.[3]
Apatite is a group ofphosphate minerals, usuallyhydroxyapatite,fluorapatite and chlorapatite, with high concentrations ofOH−,F− andCl−ion, respectively, in thecrystal. The formula of the admixture of the three most commonendmembers is written asCa10(PO4)6(OH,F,Cl)2, and the crystal unit cell formulae of the individualminerals are written as Ca10(PO4)6(OH)2, Ca10(PO4)6F2 and Ca10(PO4)6Cl2.
The mineral was named apatite by the GermangeologistAbraham Gottlob Werner in 1786,[4] although the specific mineral he had described was reclassified as fluorapatite in 1860 by the GermanmineralogistKarl Friedrich August Rammelsberg. Apatite is often mistaken for other minerals. This tendency is reflected in the mineral's name, which is derived from the Greek word ἀπατάω (apatáō), which meansto deceive.[5][6]
Apatite is one of a few minerals produced and used by biological micro-environmental systems.[7] Hydroxyapatite, also known as hydroxylapatite, is the major component oftooth enamel andbone mineral. A relatively rare form of apatite in which most of the OH groups are absent and containing manycarbonate and acid phosphate substitutions is a large component ofbone material.[13]
Fluorapatite (or fluoroapatite) is more resistant to acid attack than is hydroxyapatite; in the mid-20th century, it was discovered that communities whose water supply naturally contained fluorine had lower rates ofdental caries.[14]Fluoridated water allows exchange in theteeth of fluoride ions forhydroxyl groups in apatite. Similarly, toothpaste typically contains a source of fluorideanions (e.g. sodium fluoride,sodium monofluorophosphate). Too much fluoride results indental fluorosis and/orskeletal fluorosis.[15]
The primary use of apatite is as a source of phosphate in the manufacture offertilizer and in other industrial uses. It is occasionally used as a gemstone.[27] Ground apatite was used as a pigment for theTerracotta Army of 3rd-century BCE China,[28] and inQing dynastyenamel formetalware.[29]
Fluoro-chloro apatite forms the basis of the now obsolete halophosphorfluorescent tube phosphor system.Dopant elements of manganese and antimony, at less than one mole-percent — in place of the calcium and phosphorus — impart the fluorescence, and adjustment of the fluorine-to-chlorine ratio alter the shade of white produced. This system has been almost entirely replaced by thetri-phosphor system.[31]
Apatites are also a proposed host material for storage ofnuclear waste, along with other phosphates.[32][33][34]
Apatite is infrequently used as agemstone.Transparent stones of clean color have been faceted, andchatoyant specimens have beencabochon-cut.[3] Chatoyant stones are known ascat's-eye apatite,[3] transparent green stones are known asasparagus stone,[3] and blue stones have been calledmoroxite.[35] If crystals ofrutile have grown in the crystal of apatite, in the right light the cut stone displays a cat's-eye effect. Major sources for gem apatite are[3] Brazil, Myanmar, and Mexico. Other sources include[3] Canada, Czech Republic, Germany, India, Madagascar, Mozambique, Norway, South Africa, Spain, Sri Lanka, and the United States.
Thestandard enthalpies of formation in the crystalline state of hydroxyapatite, chlorapatite and a preliminary value for bromapatite, have been determined by reaction-solutioncalorimetry. Speculations on the existence of a possible fifth member of the calcium apatites family, iodoapatite, have been drawn from energetic considerations.[40]
Structural andthermodynamic properties of crystal hexagonal calcium apatites, Ca10(PO4)6(X)2 (X= OH, F, Cl, Br), have been investigated using an all-atom Born-Huggins-Mayer potential[41] by amolecular dynamics technique. The accuracy of the model at room temperature and atmospheric pressure was checked against crystal structural data, with maximum deviations of c. 4% for the haloapatites and 8% for hydroxyapatite. High-pressure simulation runs, in the range 0.5–75 kbar, were performed in order to estimate the isothermal compressibility coefficient of those compounds. The deformation of the compressed solids is always elastically anisotropic, with BrAp exhibiting a markedly different behavior from those displayed by HOAp and ClAp. High-pressure p-V data were fitted to the Parsafar-Mason equation of state[42] with an accuracy better than 1%.[43]
The monoclinic solid phases Ca10(PO4)6(X)2 (X= OH, Cl) and the molten hydroxyapatite compound have also been studied by molecular dynamics.[44][45]
Moon rocks collected by astronauts during theApollo program contain traces of apatite.[46] Following new insights about the presence of water in the moon,[47] re-analysis of these samples in 2010 revealed water trapped in the mineral ashydroxyl, leading to estimates of water on the lunar surface at a rate of at least 64 parts per billion – 100 times greater than previous estimates – and as high as 5 parts per million.[48] If the minimum amount of mineral-locked water was hypothetically converted to liquid, it would cover the Moon's surface in roughly one meter of water.[49]
Apatite is the prototype of a class of chemically, stoichometrically or structurally similar minerals, biological materials, and synthetic chemicals.[52] Those most similar to apatite are also known as apatites, such aslead apatite (pyromorphite) and barium apatite (alforsite). More chemically dissimilar minerals of the apatite supergroup includebelovites,britholites,ellestadites andhedyphanes.
Apatites have been investigated for their potential use as pigments (copper-doped alkaline earth apatites), asphosphors and for absorbing and immobilising toxic heavy metals.
Furthermore, compensating substitution of monovalent and trivalent cations for calcium, of dibasic and tetrabasic anions for phosphate, and of the balancing anion, can occur to a greater or lesser degree. For example, in biological apatites there is appreciable substitution of sodium for calcium and carbonate for phosphate, in belovite sodium andcerium orlanthanum substitute for a pair of divalent metal ions, in germanate-pyromorphitegermanate replaces phosphate and chloride, and in ellestadites silicate and sulphate replace pairs of phosphate anions. Metals forming smaller divalent ions, such as magnesium and iron, cannot substitute extensively for the relatively large calcium ions but may be present in small quantities.[54]
^According to Werner himself – (Werner, 1788), p. 85 – the name "apatite" first appeared in print in:
Gerhard, C.A.,Grundriss des Mineral-systems [Outline of the system of minerals] (Berlin, (Germany): Christian Friedrich Himburg, 1786),p. 281. From p. 281:"Von einigen noch nicht genau bestimmten und ganz neu entdeckten Mineralien. Ich rechne hierzu folgende drei Körper: 1. Den Apatit des Herrn Werners. … "(On some still not precisely determined and quite recently discovered minerals. I count among these the following three substances: 1. the apatite of Mr. Werner. … )
Werner described the mineral in some detail in an article of 1788.
Werner, A.G. (1788)"Geschichte, Karakteristik, und kurze chemische Untersuchung des Apatits" (History, characteristics, and brief chemical investigation of apatite),Bergmännisches Journal (Miners' Journal), vol. 1, pp. 76–96.On pp. 84–85, Werner explained that because mineralogists had repeatedly misclassified it (e.g., asaquamarine), he gave apatite the name of "deceiver":"Ich wies hierauf diesem Foßile, als einer eigenen Gattung, sogleich eine Stelle in dem Kalkgeschlechte an; und ertheilte ihm, – weil es bisher alle Mineralogen in seiner Bestimmung irre geführt hatte, – den NamenApatit, den ich von dem griechischen Worteαπατάω (decipio) bildete, und welcher so viel asTrügling sagt." (I then immediately assigned to this fossil [i.e., material obtained from underground], as a separate type, a place in the lime lineage; and conferred on it – because it had previously led astray all mineralogists in its classification – the name "apatite", which I formed from the Greek wordαπατάω [apatáō] (I deceive) and which says as much as [the word] "deceiver".)
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