APATITE, a widely distributed mineral, which, when found in large masses, is of considerable economic value as a phosphate. It was named from the Greek 6.7rarav, to deceive, because it had previously been mistaken for other minerals, such as beryl, tourmaline, chrysolite, amethyst, etc. Two chemical varieties of apatite are to be distinguished, namely a fluor-apatite (CaF) , and a chlor-apatite Apatite frequently occurs as beautifully developed crystals, sometimes a foot or more in length, belonging to that class of the hexagonal system in which there is pyramidal hemihedrism. In this type of sym metry, of which apatite is the best example, there is only one plane of symmetry, which is perpendicular to the hexad axis.
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, etc. Hardness 5, specific gravity 3.2.
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 minute acicular crystals. The extensive deposits of chlor-apatite near Kragero and Bamle, near Brevik, in southern Norway, are in connection 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 connection with granite and veins of tin stone is, on the other hand, a fluor-apatite. Special mention may be made here of the beautiful violet crystals of fluor-apatite which occur in the veins of tin-ore in the Erzgebirge, and of the bril liant 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 crystal line limestones; in eastern Canada extensive veins of apatite occur in the limestones associated with the Laurentian gneisses.
(L. J. S. )