Apatite

Apatite (Gr. apatē, 'deception'), a mineral so named because it resembles various other minerals for which it might be mistaken, consisting chiefly of phosphate of lime. The different varieties of apatite contain a little fluoride or chloride of calcium, or both, as well as phosphate of lime. Of these varieties, besides those already mentioned, there are others, as Moroxite, Francolite, and Asparagus Stone. It occurs both massive and in crystals—which are generally small, and are often six-sided prisms, or six-sided tables, but some very large ones have been brought from Canada. It occurs in some of the tin mines in Cornwall, Saxony, Bohemia, &c., and in rocks of various ages, as mentioned above. It is found of various colours, more or less green, blue, or red, sometimes white, and often gray. It frequently occurs, generally in the form of small needles, as a rock-constituent, in such rocks as granite, dolerite, diorite, &c. The massive radiated variety of apatite is called phosphorite, and when massive, earthy, and impure, is known as osteolite. These massive varieties may occur in veins, beds, or irregular masses, and are perhaps most abundantly met with amongst the archæan rocks. At Estremadura, in Spain, they occur in cretaceous strata. These mineral phosphates of lime have been much used in the preparation of manures, but as they generally require expensive mining and reduction, their production has to some extent fallen off—the most abundant supplies of lime-phosphates being at present obtained from phosphatic nodules or Coprolites (q.v.). Commercially, any natural lime-phosphate is known as apatite. Hence phosphatic nodules, and the interesting 'rock-guano,' called osite or Sombrerite, are alike spoken of as apatite. Sombrerite has been obtained in large quantities from the small island of Sombrero, to the east of the Virgin Islands, in the British West Indies. It is now believed that this hard or rock guano has been formed by water filtering through ordinary guano into the coral rock adjoining, and turning it more or less completely into phosphate of lime. The general treatment to which mineral phosphate is subjected is to reduce it to powder, and act upon the pulverised matter with sulphuric acid, which renders the phosphoric acid in the apatite soluble in water. See MANURE, LIME, PHOSPHORUS.