Use running water – Run for a few minutes under a stream of running water.
Make sure your crystals are not fragile or porous, for example selenite or desert rose which dissolve in water. If unsure, you can check online for the Mohs scale of hardness. Look for a 5 or above, with some caveat
Place in moonlight – Place in a dish or bowl on a windowsill overnight where the crystal will be in moonlight.
Place in sunlight – Place in a dish or bowl on a windowsill and let the crystals soak up the sun. Be cautious of some crystals which can generate heat in the sun and start a fire, for example clear quartz.
Place the crystal with other cleansing stones – Some stones do not need to cleansed, such as amethyst, clear quartz and citrine. These “super crystals” can be placed by other crystals to clear them.
Place them in a geode – If you have a crystal geode you could place the crystals directly onto or inside the geode.
Smudge – You could burn sage in a bundle or incense
and pass through the smoke.
Tibetan Bowl – Place crystals in a Tibetan bowl and ring several times.
Sea Salt – Place in a bowl of sea salt. Be cautious with this method as the salt can be abrasive and scratch the crystals.
Flowers – Place in a bowl of flower petals.
In the ground – bury the crystals in the Earth for cleansing.