Gold is the most malleable, yet also the most resistant to environment metal known to man. Because of those two qualities, it has been the first metal used by mankind (as far as 4th millenium BC at least), and also the one considered the most desirable of precious metals. Its value has been used as the standard for many currencies (known as the gold standard) in history. Gold has been used as a symbol for purity, value, royalty, and particularly roles that combine these properties. Most of the gold ever mined stayed in circulation indefinitely, objects made from it melted time and time again.