Cobalt finds its largest use in the form of cobalt salts, employed in coloring pottery and glass and in insect poisons. Cobalt is also used in some of the best high-speed tool steels. "Stellite," which is used to a limited extent in non-rusting tools of various sorts, and in considerable quantity to replace high-speed tool steels, is an alloy of cobalt, chromium, and small quantities of other metals. Considerable experimental work has been done on the properties and uses of cobalt alloys, and their consumption is rapidly on the increase. Cobalt is an item of commerce of insignificant tonnage. There are only two countries, Canada (Ontario) and the Belgian Congo, which produce noteworthy amounts. The Katanga district in the Congo produces blister copper that contains as much as 4 per cent of cobalt, though usually less than 2 per cent. This product formerly went to Germany, and now goes entirely to Great Britain. Just how much cobalt is saved is unknown, but probably several hundred tons annually. It is probable that most of the cobalt in these ores will be lost on the installation of a leaching process for recovery of the copper. Canada exports most of its product to the United States, though the amount is small. Domestic production in this country has been too small to record. The United States has been dependent on imports from Canada. GEOLOGIC FEATURES The principal cobalt minerals are smaltite (cobalt arsenide), cobaltite (cobalt-arsenic sulphide), and linnaeite (cobalt-nickel sulphide). Under weathering conditions these minerals oxidize readily to form asbolite, a mixture of cobalt and manganese oxides, and the pink arsenate, erythrite or "cobalt bloom." Cobalt minerals are found principally in small quantities disseminated through ores of silver, nickel, and copper. The production of Canada is obtained mainly as a by-product of the silver ores of the Cobalt district (described on pp. 234-235), and smaller amounts are recovered from the Sudbury nickel ores (pp. 180-182). The cobalt of Belgian Congo is obtained from rich oxidized copper ores which impregnate folded sediments (p. 205). MERCURY (QUICKSILVER) ORES ECONOMIC FEATURES