Some techniques for identifying a gemstone include basic observation, assessment of the stone's physical characteristics or morphology, and use of chemical and physical tests to determine specific gravity, light dispersion, color changes and refractive index. The data gathered from the evaluation are used to make a positive gem identification.
Gem stones usually have a crystalline structure, and each gem is made up of distinct crystal particles that are unique to its species. In terms of color, the stone's hue, saturation and tone are major identifying markers. The Gemological Institute of America has 31 hues in its reference color wheel and seven tone levels, from very light to very dark.