Residuum?

[Excession]

Personally, I've just ruled that gold and residuum are the same thing. Residuum is what you get when you take gold and remove all the metal bits. You can also use gold coins directly in rituals, you just end up with a lot of worthless burned up iron coins or something afterwards.

Platinum is just the same thing, but with more residuum stuffed in the gaps between the atoms.

This is then what makes gold a valuable product in my world. After all, without being literally made out of magic, why would gold be worth anything? Sure it's pretty, but it's too soft to make anything useful out of