I never understood why diamonds and gold were of any value. Sure, they sparkle but in the end they’re rocks.
Gold is really good. It is malleable and can be mashed to a flatness that is as thin as a single atom…. It is a very good conductor of electricity and it doesn’t corrode at all. It’s pretty dense so it has some heft to it. It is pretty scarce in the world so the supply increases very slowly. Plus it is shiny and the yellow color is very pleasant. The not being able to corrode and the weight and scarcity and pleasant color make it useful as a store of value.
Tungsten which is what they used to make lightbulb filaments is almost exactly the same density as gold so one could form it into a bar and cover with gold and you would not be able to see a difference in the weight. This is called “salting” and probably a pretty large amount of the gold bars in the world are partly made up of tungsten. You can’t tell without sawing the bar into pieces.