These anhydrite crystals are from the Naica Mine in Naica, Mun. de Saucillo, Chihuahua, Mexico. It is mined for its deposits of silver, lead and zinc minerals. This mine also contains 87 different mineral species. The 50 foot selenite crystals in its “cave of swords” is worth mentioning. It is also famous for the unique blue colored anhydrite crystals found there. Anhydrite is a sulfate that contains the elements Ca and S, and O and is usually white or colorless. This piece consists of several interpenetrating clusters of blue parallel anhydrite crystals with druse calcite crystals on one side. The anhydrites are terminated and have a chatoyant pearly luster. The piece is good on all sides. This piece measures 5 x 2 3/8 x 1 1/2 inches or 128 x 60 x 38 mm.