There are already diamonds, emeralds and rubies - but rather useless in general yet (except for quests or decorations). But jewelry making will be implemented some day...
Also cinnabar and lumium - probably metallic, but not useful for crafting yet. And less useful for blacksmithing anyway, in case of cinnabar - giving quicksilver.
So it's not like there are none of those at all. But true - what you can buy from merchants, you may be able to dig for some day too. Why not blocks of salt. But more probably on lower levels, close to the Pond surface.
"Just" needs to be implemented.
