The Apatite Group – Apatite Composition, Crystallization & Structure
The Apatite Group consists of a closely relates series of minerals crystallizing in the pyranidad class of the hexagonal system. The are:
Apatite
Composition. Fluor-apatite, Ca4(CaF)(PO4)3; more rarely chlor-apatite, Ca4(CaCl)(PO4)3.
Crystallization. Hexagonal; tri-phyramidal. Crystasl usually long prismatic in habit; sometimes short prismatic or tabular.
Usually terminated by prominent pyramid of firs order and frequenty a basal plane (Figs. 348 and 349). Some crystals show fes of the third order pyramid and have at times a very complex development.
Structure. Usually crystallized; also granular massive to compac.
Physical Properties. H. = 5 (can just be scratched by a knife). G. = 3.15. Vitreous to subresious luster. Color usually some of green or brown; also blue, blue violet, colorless. Transparent to opaque.
Test. Difficultly fusible (5-5.5). Soluble in acids. Gives a yellow precipitate of ammonium phosphomolydate when dilute nitric acid solution is added to large excess of ammonium molybdate solution. Concetrated hydrochloric acid solution gives white precipitate of calcium sulphate when a few drops of sulfuric acid are added. Recognized usually by its crystals, color and hardness. Distinguished from berly by the prominent pyramid terminations of its crystals and by its being softer than a knife.
Variety. Prosphorite. An impure variety of apatite is known as phosphorite. It occurs in a compact or earthy form or in concretionary and nodular masses in fossiliferrous rocks of different ages. Probably of organic origin.
Ocurrence. Apatite is widely disseminated as an accessory contituent in all classes of rocks; igneous, metamorphic and sedimentary. If is also found in pegmatite and other veins, probably of pneumatolytic origin found titaniferous magnetites. Occasionally concentrated into large deposits or veins. In the form of phosphorite or phospate rocks occurs extensively as a rock stratum. Apatite, as it exists scattered in small crystals throughout the rocks, slowly undergoes alteration and is gradually dissolved by percolating carbonated waters. Some of the phosphoric acid thus brought into solution goes into the sea where it is absorbed by living organisms, some remains in the soil where its presence is a necessary condition for fertillity and from which it is absorbed by plants and trough them goes into the bodies of phosphorite are derived from organic sources, such as animal remains. Bone is calcium phophate in composition. Apatite occurs in commercial amount in Ontario and Quebec, Canada. It is foud there in crystals and masses enclosed in crystalline calcite and in veins and irregular nests along the contact of the limestones with eruptive rocks. The chief deposits lie in Ottawa County, Quebec. Crystalline apatite occurs in large amounts along the southern coast of Norway, between Langesund and Arendal. It is found there in veins and pockets associated with a mass of gabbro. Nodular deposits of phosphate rock are found at intervals all along the Atlantic coast from North Carolina to Florida, the chief deposits being in the latter state. High grade phosphate deposits are found in western middle Tennessee. Comercial deposits of phosphorite are to be found in Northern Africa, in Tunnisa, Algeria and Morocco.
Finely crystallized apatite occurs at various localities in the Tirol; in Switzerland; Jumilla, Spain; at Auburn, Maine; St. Lawrence Co New York; Akexander Co., North Carolina; San Diego Co., Californi, etc.
Use. Apatite and phosphate rocks are chiefly used for fertilizer purposes. They are usually ground and treated with sulfuric acid to render the phosphoric acid more soluble. Transparent varieties of apatite of fine color are occasionally used for gem material. They minerals is too soft, however, to allow of its very extensive use for this purpose.
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