Gem box

Obtaining
completing lairs and/or dungeons. It seem as if you get better stuff if you have more than a 10 stack in gem boxes

usage
the box and whatever lies in it is not tradable so the only use I see to open the box

inside
gems and gem dust

if the blue bar gets to max it gives a 100% chance of a high level gem ready for leveling or loot collecting (if it is useless)

wiki page

obtaining
it is so easy to obtain that any time you find a lair or dungeon you are almost impossible not to get one, and it seems you get more good stuff if you get more than ten (the higher the number after ten the better the stuff can get)