Each gem has a typical refractive index due to its chemical composition and crystallization structure. The gem refractometer is a primary and useful tool in identifying and authenticating polished precious and semi-precious gemstones as well as observing the optical properties and structure of gemstones. It can be used to measure R.I. to many minerals in crystal form as long as the crystals have a flat and polished face. The included contact liquid or RI oil is needed to create contact between the stone and the prism glass to measure or test the Refractive Index of faceted stones, its transparency or opacity, beauty, durability and scarcity. Through the parameters you can check if the gem is an anisotropic or an isotropic stone, uniaxial or biaxial photopositive or photonegative. The built-in LED light also aids in idenfying the refractive index (RI), quality and category of gemstones. Moreover, this gem refractometer can also be used to measure the index of double refraction. Special Features * Heavy duty, highly accurate and reliable * Compact design and lightweight Specifications * Accuracy : ±0.02 RI * Illumination : Built-in LED illumination with on/off switch * Measuring range : 1.30 - 1.81 RI * Minimum division : 0.01 RI * Contact Oil: FULL SCALE refractive index (1.81 RI) oil (included in 2ml bottle) * Filter : Polarizing filter * Power source : 3 x 4.5V button battery (included) * Item size : approx. 115 x 35 x 63mm Set Includes * 1 x Gem Refractometer (main unit) * 1 x 2ml bottle FULL SCALE refractive index (1.81 RI) oil * 3 x 4.5V button battery * 1 x Soft carrying bag * Instruction manual * Standard colored factory packaging box