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APATITE
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APATITE , a widely distributed See also:mineral, which, when found in large masses, is of considerable economic value as a phosphate. As a mineral See also:species it was first recognized by A. G. See also:Werner in 1786 and named by him from the See also:Greek airarav, to deceive, because it had previously been mistaken for other minerals, such as See also:beryl, See also:tourmaline, See also:chrysolite, See also:amethyst, &c. Although See also:long known to consist mainly of See also:calcium phosphate, it was not until 1827 that G. See also:Rose found that See also:fluorine or See also:chlorine is an essential constituent. Two chemical varieties of apatite are to be distinguished, namely a fluor-apatite, (CaF) Ca4P3O12, and a chlor-apatite, (CaCI) Ca4P3O12: the former, which is much the commoner, contains 42.3% of See also:phosphorus pentoxide (P,05) and 3.8% fluorine, and the latter 4.10 % P2O5 and 6-8% chlorine. Fluorine and chlorine replace each other in indefinite proportions, and they may also be in See also:part replaced by hydroxyl, so that the See also:general See also:formula becomes [Ca (F, Cl, OH)] Ca4P3O12, in which the univalent See also:group Ca(F, Cl, OH) takes the See also:place of one See also:hydrogen See also:atom in orthophosphoric See also:acid H3PO4. The formula is sometimes written in the See also:form 3Ca3(PO4)2+CaF2. See also:Mangan-apatite is a variety in which calcium is largely replaced by See also:manganese (up to 1o% MnO). See also:Cerium, See also:didymium, See also:yttrium, &c., oxides may also sometimes be See also:present, in amounts up to 5 %. Apatite frequently occurs as beautifully See also:developed crystals, sometimes a See also:foot or more in length, belonging to that See also:division of the hexagonal See also:system in which there is pyramidal hemihedrism. In this type of symmetry, of which apatite is the best
example, there is only one See also:plane of symmetry, which is perpendicular to the hexad See also:axis. The arrangement of the pyramidal faces n and u in fig. 2 show the hemihedral See also:character and See also:absence of the full number of planes and axes of symmetry. Fig. 2 represents a highly modified crystal from St Gotthard; a more See also:common form is shown in fig. 1, which is bounded by the hexagonal See also:prism m, hexagonal bipyramid x and basal pinacoid c.
In its general See also:appearance, apatite exhibits wide See also:variations. Crystals may be colourless and transparent or See also: Lazurapatite is a sky-blue variety found as crystals with lapis-lazuli in See also:Siberia; and moroxite is the name given to dull greenish-blue crystals from See also:Norway and See also:Canada. Francolite, from Wheal Franco, near See also:Tavistock in See also:Devonshire, and also from several Cornish mines, occurs as crystallized stalactitic masses. In .14 addition to these crystallized varieties, there are massive varieties, fibrous, concretionary, stalactitic, or earthy in form, which are included together under the name See also:phosphorite (q.v.), and it is these massive varieties, together with various See also:rock-See also:phosphates (phosphatic nodules, See also:coprolites, See also:guano, &c.) which are of such See also:great economic importance: crystallized apatite is See also: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 in-variably present in small amounts as See also: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 See also:southern Norway, are in connexion with See also:gabbro, the See also:felspar of which has been altered, by emanations containing chlorine, to See also:scapolite, and See also:titanium minerals have been developed. The apatite occurring in connexion with See also:granite and See also:veins of See also:tin-stone is, on the other See also: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. See also:Special mention may be here made of the beautiful violet crystals of fluor-apatite which occur in the veins of tin-ore in the See also:Erzgebirge, and of the brilliant bluish-green crystals encrusting cavities in the granite of Luxullian in See also: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 See also:quartz lining the crevices in the See also:gneiss of the See also:Alps. Crystallized apatite is also occasionally found in metalliferous veins, other than those of tin, and in beds of See also:iron ore; whilst if the massive varieties (phosphorite) be considered many other modes of occurrence might be cited. (L. J. Additional information and CommentsThere are no comments yet for this article.
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