Ceylon is the chief source of supply of the best grades of crystalline graphite, viz., vein graphite. The crystalline graphite obtained in Madagascar, Bavaria, and in small quantities in the United States, Canada, Norway, Sweden, Japan and Chosen is chiefly of the flake variety and for that reason it is considered by manufacturers inferior in grade to that obtained in Ceylon. Large undeveloped deposits are reported in Greenland and Brazil. The discovery of the large deposits of flake graphite in Roumania was reported some time since. From time to time discoveries are reported from other localities but the importance is questionable, chiefly because the deposits are usually situated in places difficult to reach. It is believed that the Ceylon deposits have passed the maximum of their production and if deposits of vein graphite of equal grade and richness could be found, Ceylon producers might be hard pressed. During the last few years Madagascar has become the leading producer of crystalline graphite, and the influence of this potential supply should exert a stabilizing effect on prices of Ceylon graphite.
Austria, Chosen, Mexico, Italy and the United States are the principal producers of amorphous graphite; Chosen and Mexico supply most of the pencil graphite of the world.
The development of the electric furnace will no doubt decrease the demand for crucibles in steel making.
Great Britain, through sovereignty over Ceylon and Canada, and France, through sovereignty over Madagascar, control politically the world’s most important deposits of crystalline graphite. Japan controls the deposits of Chosen.
American capital controls the deposits of the United States, the deposits of Mexico, and in part the deposits of Canada. The Ceylon deposits have been worked mainly by small local owners, who opposed until a few years ago the attempts of an English company to gain control through the erection and operation of a modern plant. The Graphites Maskar, owning a part of the Madagascar deposits, is a subsidiary of a British company, the Morgan Crucible Co. Another large Madagascar company before the war had its main office in Hamburg, Germany. Other companies are controlled by Belgian and French capital. British interests own a part of the Italian and probably a part of the Spanish deposits.
CHAPTER XXIII
MICA
By Durand A. Hall
USES OF MICA
Two varieties of mica are of particular economic importance: muscovite or white mica, and phlogopite or amber mica. Three other varieties, lepidolite, zinnwaldite and biotite, find occasional commercial use.
Mica is marketed as sheet or block mica, mica splittings, thin sheets split chiefly from smaller sizes of block mica, and scrap or ground mica. The uses to which sheet or block mica may be put depend upon the size, thickness and shape of the piece which can be cut from it and the quality of the material itself. Factors entering into the quality of mica are: presence or absence of stains, spots, inclusions, cracks or pin holes; flexibility and elasticity; hardness; degree of distortion of the sheets; transparency; and dielectric strength.
An essential use of sheet or block muscovite is in electrical work; from the mica are made condensers for radio equipment, magnetos and certain telephone equipment; also to a less extent for resonators in sounding boxes. This mica is also used in making spark plugs, particularly plugs in high-compression engines, for winding cores and as washers in place of porcelain. These uses were widely extended by the war to meet requirements for motor transport, airplanes and radio equipment.