Impurities.-The properties of iron and steel, like those of most of the metals, are profoundly influenced by the presence of small and sometimes extremely small quantities of certain impurities, of which the most important are phosphorus and sulphur, the former derived chiefly from apatite (phosphate of lime) and other minerals which accompany the iron ore itself, the latter from the pyrite found not only in most iron ores but in nearly all coal and coke.
The artificial preparation of minerals, especially of apatite and isomorphous minerals and of crystalline oxides, was another subject in which he made many experiments.
- Those varieties of native calcium phosphate which are not distinctly crystallized, like apatite, but occur in fibrous, compact or earthy masses, often nodular, and more or less impure, are included under the general term phosphorite.
The ultimate source of these mineral phosphates may be referred in most cases to the apatite widely distributed in crystalline rocks.
The first mode of occurrence is of little significance practically, for the crystalline rocks generally contain too little phosphate to be valuable, though occasionally an igneous rock may contain enough apatite to form an inferior fertilizing agent, e.g.
Another group of phosphatic deposits connected with igneous rocks comprises the apatite veins of south Norway, Ottawa and other districts in Canada.
From 1500 to 3500 tons of apatite are obtained yearly in Norway from these veins.
In Ontario apatite has been worked for a long time in deposits of similar nature.
Thus the sulphate constitutes the minerals anhydrite, alabaster, gypsum, and selenite; the carbonate occurs dissolved in most natural waters and as the minerals chalk, marble, calcite, aragonite; also in the double carbonates such as dolomite, bromlite, barytocalcite; the fluoride as fluorspar; the fluophosphate constitutes the mineral apatite; while all the more important mineral silicates contain a proportion of this element.
FLUORINE (symbol F, atomic weight iv), a chemical element of the halogen group. It is never found in the uncombined condition, but in combination with calcium as fluor-spar CaF2 it is widely distributed; it is also found in cryolite Na3A1F6, in fluor-apatite, CaF 2.3Ca 3 P 2 O 8, and in minute traces in seawater, in some mineral springs, and as a constituent of the enamel of the teeth.
From these rocks in the Ottawa valley are quarried or mined granite, marble, magnificent blue sodalite, felspar, talc, actinolite, mica, apatite, graphite and corundum; the latter mineral, which occurs on a larger scale here than elsewhere, is rapidly replacing emery as an abrasive.
The ordinary accessory minerals of igneous rocks, apatite, in Great Britain and the continent of Europe.