"Crystal healing is a type of alternative therapy that involves using
gemstones to bring balance to an individual's life and mind. Crystals
are said to "have a stable and unchanging energy pattern, each with a
unique frequency and energy field, or resonance" that gives them special
properties, explains Judy Hall, in her work, The Little Book of Crystals. As a result, "they act like tuning forks," helping bring "harmony" to the "very unstable energy field of the human body".
(https://www.harpersbazaar.com/uk/beauty/fitness-wellbeing/a43244/crystal-healing-beginners-guide/)