Favourite gemstone or mineral and why

[user 4386]

for interest, a good indicator of rare & valuable metal prices
Rare World Metals Mint doesn't sell Osmiridium as its not a pure metal, but they do the 2 pure metals
https://www.rwmmint.com/

Yes, that is what I quoted. However it is a bit meaningless, because of the cost of refining to get the pure metals, and because nuggets are so rare that they get a much better price.