What is crystal energy in spiral knights

Crystal energy is a secondary currency is Spiral Knights. Like your Mist Energy, which regenerates over a 22 hour period, Crystal Energy, or 'CE' can be used to power certain objects, elevators, machines, doors and the like. However, CE is also tradeable, unlike CE, but is NOT regenerating.
To get it, you either need to pay money for it, or buy it from the market with Crowns, or 'CR', the standard currency of the game.