Crystal Healing involves the use of stones that are believed to store positive energy. Some are so strong and powerful that their vibration can shift the energy in a room. Stones are believed to generate a healing vibration that acts upon the body and can act as a conduit for healing from the practitioner to the recipient. Crystal therapy can be used alone or in conjunction with Reiki. When used with Reiki, crystals can increase the effectiveness of the treatment. Crystal therapy is very individualized and is discussed in advance with the client. Richard Gerber, MD writes in Vibrational Medicine, "It is believed that crystals are natural purifiers of subtle energies because they absorb negative energies and transmit only those frequencies of a positive, beneficial nature".