Depleted crystals, are vis crystals, sometimes produced by the thaumic infuser when infusing something with a vis crystal. It has a one in three chance of getting produced. It has the shape of any other vis crystal, however it has lost it's magical capabilities. It will look dull and gray. If you want to, you are able to put the depleted crystal into the thaumic crystalizer and the crystal will become once again a vis crystal.
A depleted crystal