Gold (Au) is a metallic element, known since prehistoric times. Chemically inactive, this very ductile and most malleable metal can be beaten into thin sheets of gold leaf. Only silver and copper conduct electricity better. Gold is usually hardened by alloying with other metals; it also often occurs in nature as an alloy. The gold content of an alloy is stated in carats. By definition, pure gold is 24 carats, and thus a 75 percent gold alloy is 18 carats. Gold is found widely distributed, mostly in metallic form as dust, grains, flakes, or nuggets. It occurs in quartz veins or lodes, usually in association with silver or other metals, and in alluvial placer deposits. Chief producers of gold are South Africa, Russia, Canada, and the U.S. Possibly the first metal used by humans, gold was valued for ornaments, and magical powers were attributed to it. Alchemists of the Middle Ages tried to transmute baser metals into gold. The search for gold stimulated European exploration of the Western Hemisphere.
