Selenite is known as a self cleansing stone. 
It also amplifies and charges any other spiritual tools(crystals, cards, pendulums, etc) it comes into contact with. 
Charge this piece at least once or twice a week by leaving it in the sun. 
Black tourmaline and white agate. 
This piece is not only ideal for protecting your energy but also getting rid of any negative or stagnant energy.