Step 3: Practical Gemology

Lesson 1

A dichroscope is one of the most useful instruments a gemologist can have. Its primary purpose is to determine the pleochroism of a gem. This can be a valuable piece of information in determining a gem’s identity. While you can observe pleochroism with a polariscope, it is much easier to see with the dichroscope.

The dichroscope also helps by confirming other test results. Occasionally a refractometer or polariscope will give ambiguous readings. The dichroscope can clarify that information. For example, it is often difficult to tell if you are seeing anomalous double refraction (ADR) in red and purple stones. If you find pleochroism with the dichroscope, you can be sure the stone is doubly refractive. It can also distinguish between a uniaxial or biaxial gem, something that cannot always be determined by other instruments.

See Using a Polariscope for more information on this gemology tool.


All gems, except those in the isometric system, are doubly refractive. That means that light entering the gem is split. These new beams of light have different refractive indexes and are frequently different colors. The colors may just be a subtle difference in shade or…