The Gem Refractometer , commonly known as Gemstone Refractometer, is the primary and most powerful tool in identify and authenticate polished precious and semi-precious gemstones and observing the optical properties and the structure of gemstones. This model is just as good as the expensive models used in gemological institutes. With the aid of Contact liquid (RI Fluid), that will create an optical contact between the glass and the gemstone, you can measure or test the Refractive Index of faceted stones, transparency or opacity, and its beauty, durability and scarcity. The refractive index (RI) of a gemstone provides the single most important piece of information to a gemologist seeking to identify an unknown stone. Due to its chemical composition and crystallization structure, each gem has a typical refractive index. In fact, you can also use this tool to measure R.I. for many minerals in crystal form as long as the crystals have a flat and polished face. Through these parameters, you can determine whether the gem is a Single Refraction (Isotropic) or Double Refraction (Anisotropic or Birefringence). Plus an option to get an extra bottle of 1.800 Refractive Index Oil just by adding a small amount to your order, see Available Options.