I believe gemstone mining will be one of the early exports from Luna.
Donald Franck

My take is that, initially, both lunar and Martian rocks will be a great source of value. Martian samples could sell at around $10M per gram, considering the costs of return missions that have been considered (that’s also the low-end cost of the Red Dragon sample return mission). You could use them for research, but people would definitely collect them. Once the initial rush for collector samples disappears, you can turn to jewelry.

Downside is though that the interest will quickly fade over time, as access becomes cheaper and the samples turn into a commodity. Since they are literally all over the place in both Moon and Mars, the only ones that will retain value will be those returned first. For the Moon it’ll be probably those of the Luna and Apollo missions, and maybe the very first ones returned privately. That’s why I didn’t include them as a resource for a self-sustaining economy.