Step 3: Practical Gemology

Lesson 3

Sometimes, refractive index (RI) and specific gravity (SG) readings alone won’t identify gemstones. More often than not, you’ll need a spectroscope to make a final determination. In a few cases, you can make identifications solely with this fundamental piece of gemological lab equipment. (That saves quite a bit of time). This tool is also a great asset for examining rough gems, when getting RI readings is difficult. Last but not least, sometimes only a spectroscope can distinguish if a gem’s color is natural, dyed, or irradiated.

As with all the other instruments in your gemology lab, practice makes mastery. The more you use your spectroscope, the more you’ll see and the easier it becomes.

What Does a Spectroscope Show?

Selective Absorption

Natural, white light contains all the hues of the rainbow. Colored gemstones absorb some of the light that passes through them or reflect it from their surface. This process is called selective absorption. A spectroscope will show you the wavelengths of light emitted, or reflected, from a gem. The absorbed wavelengths of light, on the other hand, will appear as a darker shade of color or…