These locations reflect the meridians of acupuncture and Ayurvedic medicine. Some crystals have the power to bend or refract light. When a ray of white light is shined through a prism, the light is divided into all the colors of the rainbow. Crystals in quartz have that same ability. There is no scientific evidence that they can identify or cure any illness.
Crystal healing serves no medical or scientific purpose.
Despite these facts, however, some healers continue to claim that carrying crystals in one's pocket, wearing them on a chain around the neck, or placing them around the house brings the power of healing within reach. Some people believe this and purchase the stones. This is good business for the crystal shop owner. It may also be good fun or a nice hobby for the purchaser. But it is not medicine.