[104] Adapted from _Mineral Resources_, U. S., 1916, Part II, U. S. Geol. Survey, 1917, pp. 377-386. SUMMARY The principal use for zirconium ores at present is determined by the refractory properties of the oxide, zirconia. Refractory bricks and shapes for furnace linings, chemical ware, and other heat, acid, and alkali resisting articles are made of zirconia, and are finding a limited market. The recent interest in zirconium is due to the remarkable properties which it is said to impart to steel. Its real worth, or function, in that direction is yet to be definitely determined, and tests conducted by the Bureau of Mines, Bureau of Standards and others are being made to ascertain the facts. The best and most available source of supply at present is Brazil, where the natural oxide, baddeleyite, occurs in considerable quantities in the states of Minas Geraes and Sao Paulo. The deposits have not been explored sufficiently to make any reliable estimate of tonnage possible, but, judged from their surface showing, they are of vast extent. The silicate, zircon, is found in Brazil, India and in the United States in commercial quantities. The important deposits of zirconium minerals are controlled by Brazil, Great Britain and the United States, but the actual ownership of many of the deposits is unknown. This is particularly true of the oxide ores. CHAPTER XIII MONAZITE, THORIUM, AND MESOTHORIUM BY R. B. MOORE USES OF MONAZITE Practically the only use of monazite has been as a source of thorium salts. In extracting these, by-products are recovered, such as cerium, lanthanum, and other rare earths. Thorium salts are used almost exclusively for the manufacture of Welsbach mantles, which consist of 99 per cent. thorium oxide and 1 per cent. cerium oxide. For this use there is no known substitute. The one other use of thorium salts is in ordinary chemical laboratories, but this use is very limited. The fluoride and other salts of cerium are used in connection with the flaming arc, their presence giving increased luminosity. Mesothorium is a radio-active element always found in thorium minerals. Until quite recently it has been thrown away in the manufacture of thorium nitrate; but it is now being produced as a by-product, and is useful as a substitute for radium in luminous paints, and for therapeutic purposes. GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION The principal sources of monazite are Brazil and India, although it has been mined successfully in the United States in the Carolinas and in Idaho. It has been found in Swaziland, Africa, and in Australia, and also, to a limited extent, in native rock and in placers in Ekaterinburg, Russia.