I use the following methods of cleansing gemstones, and even tarot
cards. I don't think it's absolutely necessary, but it makes me happier
if I do it.
1. Most often, I send Reiki energy into the object. If you don't practice
Reiki, you can brush your fingers over the gemstone in a sweeping-type
motion while repeating something like, " I remove and cleanse all previous
energies from this gemstone". Then hold the gemstone between your
palms; imagine your aura merging with the stone so it will be attuned to
your personal energy.
2. Cleanse the gemstone using the 4 elements.
Earth: sprinkle with salt or rest the stone next to a quartz crystal
Air: pass the stone through the smoke from incense
Fire: pass the stone over a candle flame
Water: sprinkle the stone with water
3. The Full Moon is thought to be a healer and cleanser. On the night of
a full moon, you can leave the gemstone on your windowsill or, weather
permitting, outdoors to soak up the moon's rays.
HTH