Optical crystals come in a wide variety of types, each with their own unique properties and characteristics. Some of the most commonly used optical crystals include calcium fluoride (CaF2), magnesium fluoride (MgF2), quartz (SiO2), sapphire (Al2O3), and potassium dihydrogen phosphate (KDP). These crystals are used for a range of applications, such as laser optics, polarizers, and optical filters, among others. The choice of crystal type depends on factors such as the required optical properties, the operating conditions, and the manufacturing process, among others.