Cobalt is named from the German Kobald, goblin or evil spirit, and was discovered in 1735. Cobalt occurs in the minerals cabaltite, smaltite, and erythrite, and is most associated with nickel, silver, lead, copper and iron ores from which it is most frequently obtained as a by-product. Important ore deposits are found in Zaire, Canada and Morocco. Cobalt is a brittle, hard metal closely resembling iron and nickel in appearance. It is alloyed with iron, nickel and other metals to make Alnico, an alloy of unusual magnetic strength with many important uses. Alloys containing cobalt, chromium and tungsten are used for high speed, heavy duty, high temperature cutting tools, and for dies. Cobalt is also used in other magnet steels and stainless steels, and in alloys used in jet turbines and gas turbine generators. Cobalt-60, an artificial isotope, is an important gamma ray source, and is used extensively as a tracer and radiotherapeutic agent.