Crystals were created as the earth formed and they have continued to metamorphose as the planet itself has changed. Crystals are the earth's DNA, a chemical imprint for evolution. They are miniature storehouses, containing the records of the development of the earth over millions of years, and bearing the indelible memory of the powerful forces that shaped it. Some have been subjected to enormous pressure, others grew in chambers deep underground, some were laid down in layers, others dripped into being, - all of which affects their properties and the way they function. Whatever form they take, their crystalline structure can absorb, conserve, focus, and emit energy, especially on the electromagnetic waveband.
(Crystal Bible - A definitive guide to crystals, Judy Hall, A Godsfield Book)