Originally Posted by
agentnone
You are correct. If they soul gem is empty, it won't be available for enchanting. If they are empty, their description will say: Petty Soul Gem. But, IIRC, if they have a soul in them, they'll say this instead: Petty Sould Gem (Petty). Also, looking in your equipment and highlighting on the gems will give you the same information. Give that a shot. I'm not an expert on enchanting whatsoever. I haven't actually done it yet myself. But I have noticed the plethora of soul gems I have, some say they have a soul in them in parenthesis and the empty ones done.