A bit of info from the net:
Many people begin their relationship with a new crystal by cleansing it first. Cleansing can also be performed at any time to refresh the crystal, clear it of any residual unwanted energies, and “re-charge” it.
There are a few exceptions for me personally – such as Quartz from Nepal and Tibet. I get these Quartz Crystals in their raw form right out of the ground, with the dirt still on them, and I don’t clean them. These particular crystals come from the Himalayan Mountains, and hold a very ancient energy full of wisdom and history. Although they may not look as aesthetically pleasing to the eye, their powerful, complex energy is amazing, and I feel the dirt from their environment adds to their intensity. At times you may find crystals or stones that you also feel the same way about. Or perhaps on a hike or trip you have found a stone along the way, and when you bring it back home with you, you would like to preserve it in its natural state as you found it, so you can enjoy it and “re-experience” that time.
There are also a few exceptions when it comes to immersing a stone in water for long periods. You should not immerse Halite in water – Halite is salt crystals, and will dissolve in water. Selenite will also degrade over a long period of time in water – it is o.k. to immerse it for a few hours or rinse it, but do not leave it in water for long periods. Some softer crystals and minerals are also sensitive to hot water, and can fracture. This is just one reason why it is good for you to educate yourself on the physical properties of the stones and crystals that you intend to work with.
Some methods of cleansing:
Water is a universal cleanser. If you have access to the ocean, ocean water is wonderful. If not, spring water, lake water, and filtered water can also work well, as long as the water is either directly from nature or clean (filtered properly.) Some people also add salt to their water, because of its electric properties.
You can simply rinse the crystal in water, or you can follow up by placing the crystal in a clear glass filled with water. Place the glass on your windowsill, ideally facing the south, to charge in the sun.
The Moon can also be used for cleansing and charging. Some people make a ritual of burying their crystal under a full moon, to take advantage of the magnetic forces of the moon in combination with the earth. You may also place your crystal in the direct light of the moon.
Another method is smudging the crystal with sage, incense, or sweet grass.
You can also cleanse and charge your crystal with other crystals. A crystal can be placed on a large crystal cluster or generator (single large quartz crystal.) Citrine in particular is excellent for cleansing the other crystals in your collection. It is one of only two crystals that is automatically self-cleansing, and will cleanse other crystals. The other is Kyanite, which is also extremely helpful in chakra alignment
