The vibrations of a crystal can be influenced/altered by changes in their surroundings.
A crystal can hold the energy impressions of its own journey (from its mining and treating processes to being sold in a shop).
A crystal could also retain the vibrations of other people that have handled the crystal (from healing clients, previous owner, other customers/shop keepers).
Cleansing a crystal is essential to remove any previous “programming” before attuning the crystal for your own intent.
Using uncleansed crystals can cause problems with healing and mediation experiences. It is vital to cleanse crystals between healing sessions so that a client’s ailments/energy vibrations do not get passed to the next client. If a crystal is imbued with a particular intent, the energy of the program could disrupt or influence the subconscious of meditation.
Some believe that jewellery, as well as crystals, can retain elements of previous owners energies, resulting in headaches/nausea from negative vibrations or strange dreams.
I believe that it is the vibrations of a crystal that heals people and has an affect on the energy field of its surroundings. Much like ripples in a pool of water after a splash, I feel that crystals can retain positive/negative energies from places and people which can effect/drain the energy output and vibrations of the crystal.
I believe that cleansing a crystals purifies the stone of any previous energies and restores it to its natural, neutral vibrations, making it safe to use for healing/meditation and easier to attune with a new intent.