Admittedly diamonds are not a good comparison, because they're not commonly used for investment and not fungible. Gold bullion is comparable insofar as it's use

Admittedly diamonds are not a good comparison, because they're not commonly used for investment and not fungible. Gold bullion is comparable insofar as it's used as a store of value, with scarcity controlled by natural limitations, rather than by policy. I'll admit that gold has some practical uses, such as in electronics, but that is not the primary market driving its trade or mining. Its use in jewellery I would say is just an extension of its use as a store of value; it is desirable because it is valuable. If we simply wanted a lustrous metal (as may have been an early factor in its adoption as a commonly traded precious metal) we now have many inexpensive ones to choose from -- aluminium, chromium, etc.