Gold's value is it is fairly stable. I would guess its value has been established, culturaly down through the ages. Does it have any other value than that, some industrial. If you look at other metals, aluminum used to be more valuable than gold by volume. I think 6 times as much. Platinum has had value over the ages. Its value today is driven by many industrial applications, catylitic converters and spark plugs etc. Silver too has had value over the ages. It still has a lot of industrial applications.
Diamonds and other gems have had cultural worth over the ages to. I think diamonds have their value due to Debere's slick advertising and control of production from their diamond mines. An engagment ring was'nt fashionable till aroud WW2 or after. It basically replaced a lot of 'human worth laws'. I am blanking on the exact term. Basically, if a man called off an engagement, she wasn't deamed fit for mariage. Basically, she was a social outcast, and her only real employment was prositution. I think this still is culturally embeded in Thialand.
The value of gold does vary. I think it was only $200/oz around 2000. So, it is purely speculative. Although it is failry compact and probably represents a pre-paper money way of indirectly exchanging goods.
Also, take nickle. It was refered to as the 'witches metal'. It was hard and basically worthless. The only pre-industrial application was that it was used in touch holes of blackpowder fire arms. Now a days it is worth something as an alloy to increase strength etc. in steel. Basically, a strategic metal.
Tom