Selenite is used to clear energy and it’s also good as a placeholder to recharge your crystals. 
 
Selenite is said to be a powerful healing crystal that promotes peace and calm, mental clarity, and well-being. It's also believed by some that this crystal can remove negative energy and help you connect to higher realms. There's no evidence to support the metaphysical or healing properties of crystal but we intuitively know that’s not true :)