I don't have a guide, per se, but more or less you will get whatever gems you normally get out of that type of ore. You'll get between 0 and 2 normal gems, possibly a rare gem, and sometimes some powder. You will always get something, and I think I have yet to get a rare gem without getting a normal. Most frequently is one gem and powder.
Outlands gems start with Thorium, although it's uncommon. Fel Iron, Adamantite and Khorium all give strictly Outlands gems.
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Only the exceptions can be exceptional.