You can use a tuning fork, singing bowl, a bell or chime. The sound will reset the crystal back to it original vibrational frequency.
Visualize pure white light surrounding the crystal and imagine all the negativity that the stone has collected turning into positive energy.
Lay your crystals out in the sunlight (a brightly lit window sill will also work). Be careful when choosing this method because the deep color of some crystals can fade in the sunlight.
Put your crystals out overnight in the moonlight to recharge in the special energy of the moon. The Full Moon is the brightest giving off the most energy to recharge.
Hold your crystal in running water for a few minutes or place in a bowl of salt (use sea salt) or rain water. Make sure that your crystal is safe to be cleansed this way; usually the stone must have a Moh’s hardness of 6 or more. I don’t recommend this method only because most people don’t know the Moh’s hardness of their crystal.
Pass your crystal thru the smoke of burning white sage, pass it thru several times. This cleanses all the negative energy that has become attached to the stone
Bury your crystals in the earth and leave overnight to ensure that the crystals are re-energized. You can bury it alone or wrap it in a natural fabric cloth. If using this method, make sure you know the exact spot where the crystal is buried.
All stones, especially delicate ones that cannot be placed in water, can be placed into a bowl of sea salt. Leave for a few hours.