Tools necessary for basic gem identification include tweezers, a 10x loupe, and a pen light or a similar light source. A refractometer, refractive index fluid and a polariscope also help with gem identification.
Observe the gem with your naked eye for hue, tone and saturation. Hue is the gemstone's basic color. Tone is a determination of whether the gem's color is light, dark or somewhere in between. Saturation is the intensity or strength of the color. Determine the transparency of the gem and how heavy it feels.
Use a pen light across the stone's surface to look for optical phenomena such as color change and sparkle. Assess its luster.
Determine the gemstone's refractive index and biorefringence by using a refractometer. Use a polariscope to determine if the gem is singly refractive, doubly refractive or an aggregate.
Use a reference book such as "Color Encyclopedia of Gems," "Gemstones of the World" or "Gem Reference Guide" to locate the mystery gem's color and refractive index. Each gemstone has a unique refractive index, which simplifies the process of positively identifying an unknown gem. If the refractive index leaves more than one option, the gemstone's identity can be narrowed by using the refractometer to determine the birefringence and single or double refractivity.