Hitting the base of a large piece of inexpensive crystal with some LED lights gives a remarkable and lovely effect in this howto video by DIYPerks.
The video's owner makes these hyperbolic claims which actually live up to the hyperbole for many viewers:
In this video we'll be making a stunning 'floating island' crystal tower light. On top of looking plain awesome, it is designed with RGB LEDs in mind, meaning it can be illuminated with literally any colour combination you choose. Trust me – this video is worth a watch in full.