When you buy a new crystal, it is recommended that you do crystal cleansing to neutralize the vibrations left by other people. After restoring the crystal to it's original clarity, you can then impress your own pure intentions upon it. Do crystal cleansing periodically especially if your crystals are used for healing to clear away all negativity.
Crystal Cleansing Tips
Sea Salt: Bury your crystal in dry sea salt in a small container for between 7 - 24 hours. Dont's use salt water because it can discolouring the crystal.
Sun & Water: Put the crystal in running water for a few minutes and then place in the sun to dry. Only recommended for crystals not susceptible to fading.
Music: The vibrations of a pure sound can energetically cleanse a crystal and remove the feeling of unpleasantness.
Crystals: Crystal clusters can be used to cleanse crystals. Place your crystals in the center of your cluster for hours and they will be completely cleansed.
Source : Crystalpalace