Throughout the centuries, gold was used for coinage and jewelry. It also has been part of the monetary system through the gold standard.
Like many other commodities, gold is mined. However, what makes it different is that gold is not used up. Due to its chemical composition, it cannot rust or deteriorate.
This puts an interesting twist on the supply/demand ratio. The reason for this is because, regardless of demand, supply will keep increasing. Other commodities, like oil, see the supply fluctuate.