The refractive index is an important optical property of transparent gemstones and is also an important indicator of gemstone authentication. A refractometer measures the total internal refraction of a gemstone, and can identify gemstones with RI in the range between 1.30 to 1.81. However, stones that have high RI (such as diamonds, zircons and garnets) cannot be properly identified with a refractometer. This instrument can measure the single RI and birefringence of faceted gemstones, and can also measure the RI of convex surface gemstones with point measurement.