Item used for quests, dunno which one yet. You just have to say "I will help" to the ghost woman to get this bag in ST. Some gems no drop drop off named. you may have to combine the gem with something else (maybe the robe all/all or other things) in this bag...
or try things out for yourself as items that do not belong in a combinable container to become something else will not combine and therefore you have nothing to lose.