I searched the forums and had no luck finding out if anyone had posted about gemstones... I have a sim who tried to "collect'em all" up until the day he died of old age (and he was actually very long-lived: 227 days, using the Long Life version). Anyway, I never found two types. Let me see if I can enumerate the ones I did find:
1. blue topaz
2. yellow sapphire
3. smoky quartz
4. ruby
5. emerald
6. luminorious (?) gem
7. tanzanite
8. diamond
So based on the fact that his skill sheet reported that he'd found 80%, I'm assuming there are two more I never found. And I had the collection helper thingy... I spent ages zooming in and out and had to click on every one of the rocks and queue it to be picked up so I could see what color it was. The collection helper thingy makes collectibles shoot out so much light you can't tell if it's a gemstone of a lump of iron.
Has anyone found all ten stones? Is there some secret place you find two of them?