I've got Jade and Tiger's Eye, and am on my way to craft my next large black gem. It's all done by breeding duplicates as fails from other breedings and now from crafting 2 Obsidians - just for the large blad gem.
It can be done, and frankly, I'm happy with the long term goal... I know it's gonna make me happy when I finaly craft the Onyx I'm still missing
What I do miss tho, is the possibility to split large gems into small ones. I've got lots of large blue gems, but almost none small blue gems. So now I had to evolve and trade useles duplicates just to get small blue gems for the dust. Would have been reasonable if I just could use the large blue gems.