Apatite

The apatites train a family of Phosphate S hexagonal of rather variable composition, Ca5 (PO4) 3 (OH, Cl, F). One classifies them in hydroxyapatites (“Hap”), chlorine-apatites (“Cl-ap”) and fluorine-apatites (“Fap”) according to the Anion prevail.

All comprise PO4 tetrahedrons isolated and from coordination 9 for the Calcium. Carbonate-apatites replace a PO4 tetrahedron by a group CO3OH or CO3F. The Calcium is often partially replaced by Strontium, Cérium, Manganèse and others Cation S.

Localization

Apatites are secondary, common minerals in the magmatic Roches , but their concentration is not sufficient for an industrial exploitation.

Apatites are often associated with the lodging S of Fer, which represents a serious problem for iron and steel industry : the Phosphore contained in the Minerai S of Fer passes in fact completely in the lic phase Métal: its elimination in the phase of refining of the Acier is expensive. The strong content of Phosphore was the reason of the abandonment of the “Lorraine Minette”.

The hydrothermal apatites are rarer. The pegmatitic apatites or metamorphic are of minerals of strong economic importance for their contents in rare elements more than for their phosphorus content.

Sedimentary apatites have a chemical and/or organic origin (biochemical): the “rough” raw material for the industry of the Phosphore is the Phosphorite, a phosphorous Roche sedimentary whose principal component is the carbonato-fluorapatite (“carFap”). The inorganic part of the skeletons of vertebrate is primarily carbonato-hydroxyapatite (“carHap”) and these skeletons form sediments with phosphates. The Phosphate of Calcium is soluble in environment Acide (river), but much less in one environment Alcalin (sea). Change of pH when a river is thrown in the sea produced the precipitation of the Phosphate, which contributes to turbid water of the Estuaire S.

Uses

The mineral is exploited like source of Phosphore to manufacture artificial manures. These manures can contain traces of Polonium 210 naturally present in the ore, like those used for the fertilization of the tobacco in the United States (http://en.wikipedia.org/wiki/Apatite). Apatite is also used in chemical industry. When this mineral is of quality Gemme, it can be used in jewelry (facets, cabochons). Apatite plays a key function in the Physiologie as in the pathology of the organization of the Vertébré S. All the hard fabrics of the organization - except for the hard parts of the ears - are composed of apatites; the pathological Calcification S also consist of apatite.

Apatites are used for the thermochronology low temperature in geology. Indeed, they comprise a quantity of Uranium whose isotope 238 disintegrates during time by involving a deformation of the crystal lattice (what is called a " Trace of Fission"). These traces in permance are reabsorbed if the mineral is located at an higher temperature with 100°C approximately. In on this side this temperature, they are preserved in mineral. By using the decay constant of 238U, the counting of these traces makes it possible to go back to the age of cooling of the rock, i.e. its increase in the earth's crust or its exhumation.

to see too

  • Schmittner Karl-Erich and Giresse Pierre, 1999. Microphone-environmental controls one biomineralization: superficial processes off apatite and calcite precipitation in Quaternary soils, Roussillon, France. Sedimentology 46/3: 463-476.

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