Gold is a metal element which has the atomic number 79, and an atomic weight of 196.9665. Its atomic symbol is Au which comes from its Latin name, aurum, for "shining dawn." It is relatively abundant in nature, occurring in many rocks and in seawater. Its estimated abundance in the earth's crust is 0.005 parts per million. Gold is the most malleable of elements. A single troy ounce can be hammered into a sheet that will cover 68 square feet (6.3 sq. m) only 0.00025-0.0001 inch (0.00025 cm) thick. The element is very unreactive. It is not attacked by air, oxygen, or most acids, but is dissolved by aqua regia (a mixture of concentrated hydrochloric and nitric acids) and is tarnished by sulfur.

Gold is probably the oldest of all metallic elements known to humans. The element occurs free in nature and is widely distributed. It is likely that gold was first discovered in...