Crystals need to be cleansed once in a while or after they have been used in healing, protection or in spells to rid them of any negative energies they have stored.
There are many way to cleanse your crystal and your might have your own preference.
Earth – burying your crystal
Water – allowing flowing water to run over your crystals, mineral, spring or even the sea water works well and let them dry naturally.
Fire – Place candles (tea lights are good) in a circle surrounding your crystals and let the candles burn until they go out.
Air (smudging) – you can use a bundle of sage or an incense stick in either sage or lavender and waft the incense smoke around the crystals to cleanse them.
Sun/Moon – Leaving them out in sunlight or a full moon for 12 hours
One way I like is using two bowls one smaller than the other, salt water in the outer one and the crystals in the other. Salt is a brilliant cleanser but can be to harsh on some crystals but doing this way is safe for all.