[amluto]

The actual market value of diamonds is pretty low. You can pay a jeweler a lot of money for a shiny diamond, but good luck reselling it for a similar amount of money.

Gold, OTOH, is fungible. You can melt it, mold it into different shapes bars, resell it, etc.

[jajko]

With diamond jewelry, you pay mostly for the manual work of jeweler since folks don't go to jewelry shops to buy a diamond stone alone. If we talk about gold bars, no sophisticated manual work involved, just pouring molten gold into some mold on semi-industrial automated scale.

If you buy sophisticated golden jewelry, you also pay ton for work that nobody else may appreciate. Sure you can get it smelted into something else, but you burn most of the original value, and some more on the change itself.