Have been unable to use this on any crystals I have come across. Wasn't sure if I was doing it wrong, but always get the message "You cannot use the elixir on this object"
Did you use it on the crystal on the ground, or in your inventory?
It usually works fine if it's on the ground, but not in your inventory.
This mechanic might prove more useful if explained somewhere, as it applies to poisons and other things in game as well.
I tried in inventory and on the ground. Each time was told I could not use it on the item.
I've had this work using it on the crystal inside my inventory. But that was ages ago (and not quite that useful, I might add).
I used one on the ground yesterday, it worked perfectly.