You might be interested in some threads from the FAQ section on "Why was gold always considered so valuable?":
Things gain value because we as humans attach value to them, and there are good reasons why we attach value to gold:
Gold is shiny: It may sound silly, but think of all the valuable metals, stones and gems you can think of. Diamonds, emeralds, silver etc; All they have universally in common is that they are very pretty to look at, and thus are vaunted after, especially for trades like jewellery making.
**Gold is rare:**Very rare for that matter. There's no totally agreed upon total for how much gold has ever be mined by man, but it goes something like this:
"A figure that is widely used by investors comes from Thomson Reuters GFMS, which produces an annual gold survey.
Their latest figure for all the gold in the world is 171,300 tonnes - which is almost exactly the same as the amount in our super-villain's imaginary cube.
A cube made of 171,300 tonnes would be about 20.7m (68ft) on each side. Or to put it another way, it would reach to 9.8m above ground level if exactly covering Wimbledon Centre Court.
But not everyone agrees with the GFMS figures. " (BBC News)
Thus gold is very rare, and with rarity comes value. Aluminium used to be of extreme value until the Bayer and Hall-Heroult processes made it much cheaper to produce. As another example, the value of diamonds is maintained at an artificial high by withholding mined diamonds from the market. Gold though is very rare and always has been, thus it has value.
Gold is stable: In a chemical sense gold is an extremely stable element because of its atomic layout. Being very stable adds value for several reasons; it means it can stand up to prolonged contact with air and human skin without tarnishing and will maintain its luster almost indefinitely. This makes gold very valuable as a material in jewellery. It also makes a very good form of currency because of this. If you opened a safe and found your money had rusted away, you would quickly stop attaching value to it.
Gold can be easily alloyed: Pure gold is very soft and malleable so isn't very useful for many things. When alloyed with other metals though, it becomes much harder and far more useful for things like jewellery. It will also maintain its luster well, so cheaper and less pure alloys can be used for things such as currency, whereas for more expensive purer alloys of gold can be used for applications such as ingots or jewellery.