Common crystal gems are required for the Fire Curse enchantment.
If you hold off on using the invoker jewels until you have all 5, using them together will shut down the machine and spawn a small chest with random equipment (rare quality or better; I got a set of epic leggings which I upgraded to).
If it wasn't for your second post in a row, I would not have noticed the first (edits don't get a post to show up as unread).
