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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
Streak White
Diaphaneity Transparent to translucent[2]
Specific gravity 3.16 - 3.22[2]
Polish luster Vitreous[1]
Optical properties Double refractive, uniaxial negative[1]
Refractive index 1.634 - 1.638 (+.012, -.006)[1]
Birefringence .002-.008[1]
Pleochroism Blue stones - strong, blue and yellow to colorless. Other colors are weak to very weak.[1]
Dispersion .013[1]
Ultraviolet fluorescence 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.[1]

Apatite is a group of phosphate minerals, usually referring to hydroxyapatite, fluorapatite, chlorapatite and bromapatite, named for high concentrations of OH, F, Cl or Brions, respectively, in the crystal. The formula of the admixture of the four most common endmembers is written as Ca10(PO4)6(OH, F, Cl, Br)2, and the crystal unit cell formulae of the individual minerals are written as Ca10(PO4)6(OH)2, Ca10(PO4)6(F)2, Ca10(PO4)6(Cl)2 and Ca10(PO4)6(Br)2

Apatite is one of a few minerals that are produced and used by biological micro-environmental systems. Apatite has a Mohs Scale hardness of 5. Hydroxylapatite is the major component of tooth enamel and bone mineral. A relatively rare 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 than is hydroxyapatite. For this reason, toothpaste typically contains a source of fluoride anions (e.g. sodium fluoride, sodium monofluorophosphate). Similarly, fluoridated water allows exchange in the teeth of fluoride ions for hydroxyl groups in apatite. Too much fluoride results in dental fluorosis and/or skeletal fluorosis.

Fission tracks in apatite are commonly used to determine the thermal history of orogenic (mountain) belts and of sediments in sedimentary basins. (U-Th)/He dating of apatite is also well-established for use in determining thermal histories and other, less typical applications such as paleo-wildfire dating.

Phosphorite is a phosphate-rich sedimentary rock, that contains between 18% and 40% P2O5. The apatite in phosphorite is present as cryptocrystalline masses referred to as collophane.

Contents

Uses

Apatity City, Russia, site of apatite mines and processing facilities

The primary use of apatite is in the manufacture of fertilizer - it is a source of phosphorus. It is occasionally used as a gemstone.

Fluoro-Chloro Apatite forms the basis of the now obsolete Halophosphor fluorescent 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 adjusts the shade of white produced. Now almost entirely replaced by the Tri-Phosphor system.[3]

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. This is also the source of radioactive polonium found in cigarettes.[4]

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 US. It is also used in other countries.

Use as an ore mineral

Apatite is occasionally found to contain significant amounts of rare earth elements and can be used as an ore for those metals [6]. This is preferable to traditional rare earth ores, as Apatite is non-radioactive [7] and does not pose an environmental hazard in mine tailings. Apatite is an ore mineral at the Hoidas Lake rare earth project[8].

Thermodynamics

The standard (p = 0.1 MPa) molar enthalpies of formation in the crystalline state of hydroxyapatite, chlorapatite and a preliminary value for bromapatite, at T = 298.15 K, have already been determined by reaction-solution calorimetry. Speculations on the existence of a possible fifth member of the calcium apatites family, Iodoapatite, have been drawn from energetic considerations [9].

See also

Apatite Crystal, Mexico

References

  1. ^ a b c d e f g h i j k l m n o p Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
  2. ^ a b c d http://webmineral.com/data/Apatite.shtml Webmineral data
  3. ^ Henderson and Marsden, "Lamps and Lighting", Edward Arnold Ltd, 1972, ISBN 0 7131 3267 1
  4. ^ http://www.webspawner.com/users/radioactivethreat/
  5. ^ Streeter, Edwin W., Precious Stones and Gems 6th edition, George Bell and Sons, London, 1898, p306
  6. ^ Salvi S, Williams‐Jones A. 2004. Alkaline granite‐syenite deposits. In Linnen RL, Samson IM, editors. Rare element geochemistry and mineral deposits. St. Catharines (ON): Geological Association of Canada. pp. 315‐341
  7. ^ Haxel G, Hedrick J, Orris J. 2006. Rare earth elements critical resources for high technology. Reston (VA): United States Geological Survey. USGS Fact Sheet: 087‐02. Available online from the USGS at http://pubs.usgs.gov/fs/2002/fs087-02/fs087-02.pdf
  8. ^ Great Western Minerals Group Ltd. | Projects - Hoidas Lake, Saskatchewan
  9. ^ Cruz, F.J.A.L.; Minas da Piedade, M.E.; Calado, J.C.G. "Standard molar enthalpies of formation of hydroxy-, chlor-, and bromapatite" J. Chem. Thermodyn. 37 (2005) 1061-1070

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.
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1911 encyclopedia

Up to date as of January 14, 2010

From LoveToKnow 1911

APATITE, a widely distributed mineral, which, when found in large masses, is of considerable economic value as a phosphate.. As a mineral species it was first recognized by A. G. Werner in 1786 and named by him from the Greek araTav, to deceive, because it had previously been mistaken for other minerals, such as beryl, tourmaline, chrysolite, amethyst, &c. Although long known to consist mainly of calcium phosphate, it was not until 1827 that G. Rose found that fluorine or chlorine is an. essential constituent. Two chemical varieties of apatite are to be distinguished, namely a fluor-apatite, (CaF) Ca 4 P 3 0 12j and a chlor-apatite, (CaC1) Ca 4 P 3 O 12: the former, which is much the commoner, contains 42.3% of phosphorus pentoxide (P205) and 3.8% fluorine, and the latter 4.10% P 2 0 5 and 6.8% chlorine. Fluorine and chlorine replace each other in indefinite proportions, and they may also be in part replaced by hydroxyl, so that the general formula becomes [Ca (F, Cl, OH)] Ca4P3012, in which the univalent group Ca(F, Cl, OH) takes the place of one hydrogen atom in orthophosphoric acid H 3 PO 4. The formula is sometimes written in the form 3Ca3(P04)2+CaF2. Mangan-apatite is a variety in which calcium is largely replaced by manganese (up to 10% MnO). Cerium, didymium, yttrium, &c., oxides may also sometimes be present, in amounts up to 5%. Apatite frequently occurs as beautifully developed crystals,. sometimes a foot or more in length, belonging to that division of the hexagonal system in which there is pyramidal hemihedrism. In this type of symmetry, of which apatite is the best FIG. I. FIG. 2.

example, there is only one plane of symmetry, which is perpendicular to the hexad axis. The arrangement of the pyramidal faces n and u in fig. 2 show the hemihedral character and absence of the full number of planes and axes of symmetry. Fig. 2 represents a highly modified crystal from St Gotthard; a more common form is shown in fig. 1, which is bounded by the hexagonal prism m, hexagonal bipyramid x and basal pinacoid c. In its general appearance, apatite exhibits wide variations. Crystals may be colourless and transparent or white and opaque, but are often coloured, usually some shade of green or brown, occasionally violet, sky-blue, yellow, &c. The lustre is vitreous, inclining to sub-resinous. There is an imperfect cleavage parallel to the basal pinacoid, and the fracture is conchoidal. Hardness 5, specific gravity 3.2.

Yellowish-green prismatic crystals from Jumilla in Murcia in Spain have long been known under the name asparagus-stone. Lazurapatite is a sky-blue variety found as crystals with lapislazuli in Siberia; and moroxite is the name given to dull greenishblue crystals from Norway and Canada. Francolite, from Wheal Franco, near Tavistock in Devonshire, and also from several Cornish mines, occurs as crystallized stalactitic masses. In addition to these crystallized varieties, there are massive varieties, fibrous, concretionary, stalactitic, or earthy in form, which are included together under the name phosphorite, and it is these massive varieties, together with various rock-phosphates (phosphatic nodules, coprolites, guano, &c.) which are of such great economic importance: crystallized apatite is mined for phosphates only in Norway and Canada.

With regard to its mode of occurrence, apatite is found under a variety of conditions. In igneous rocks of all kinds it is invariably present in small amounts as minute acicular crystals, and was one of the first constituents of the rock to crystallize out from the magma. The extensive deposits of chlor-apatite near Kragero and Bamle, near Brevik, in southern Norway, are in connexion with gabbro, the felspar of which has been altered, by emanations containing chlorine, to scapolite, and titanium minerals have been developed. The apatite occurring in connexion with granite and veins of tin-stone is, on the other hand, a fluor-apatite, and, like the other fluorine-bearing minerals characteristic of tin-veins, doubtless owes its origin to the emanations of tin fluoride which gave rise to the tin-ore. Special mention may be here made of the beautiful violet crystals of fluor-apatite which occur in the veins of tin-ore in the Erzgebirge, and of the brilliant bluish-green crystals encrusting cavities in the granite of Luxullian in Cornwall. Another common mode of occurrence of apatite is in metamorphic crystalline rocks, especially in crystalline limestones: in eastern Canada extensive beds of apatite occur in the limestones associated with the Laurentian gneisses. Still another mode of occurrence is presented by beautifully developed and transparent crystals found with crystals of felspar and quartz lining the crevices in the gneiss of the Alps. Crystallized apatite is also occasionally found in metalliferous veins, other than those of tin, and in beds of iron ore; whilst if the massive varieties (phosphorite) be considered many other modes of occurrence might be cited. (L. J. S.)


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