Dichroïsme is a characteristic of a uniaxial crystal showing a different colouring in the axis which is perpendicular to the optical axis..

Cleavage is a plane according to which a crystal can easily split.

A doublet is a gluing joint of two substances to imitate a gem (if more than two substances are used, the result is called triplet or quartet).

As for counterfeiting, any colour collection gem of a certain value should be examined by a certified gemology laboratory.

Anyone willing to improve his knowledge of gems should train his eye observation using a 10x magnifying glass.


For more information, click on the links (french version only) : diamond, emerald, sapphire and ruby.
For a description of the main gems : see chart