Crystal" glasses are not made out of crystal at all. The naming of certain types of glass as "crystal" is a confusing and inaccurate historical tradition. A crystal is any material that has its molecules aligned spatially into regularly repeating patterns. Metals, ceramics, salts, ice, sugar, and rocks are all crystal. "Crystal" glass is not. In fact, the term "crystal glass" is a pure oxymoron. By definition, glasses are materials that have their molecules unordered. In other words, the very definition of glass is a material that is not a crystal.