Angelite is a form of anhydrite, which is a crystal made of calcium sulfate. The crystals are formed in places where gypsum stones had previously been in contact with water, which then evaporates, leaving anhydrite crystals behind. The stone is formed from celestite (another form of gypsum) that has been compressed for many millions of years. Anhydrite gypsum was originally found in Peru. It has since been found in Britain, Germany, Poland, Libya, Egypt and Mexico.