Helpful Information: Zircon is a gem that has a strong double refraction which means that it divides light into two pathways within the gem due to its molecular structure. When looking at a zircon through the table, the back facets will be doubled, as if mirrored. This can be seen with the unaided eye; it is very obvious. Zircon is also very brilliant, nearly as much as diamond and produces a very bright, showy gem. It is brittle and must be set carefully in jewelry and worn with care. This gem has been known since ancient times and has been appreciated and used as a diamond substitute in its colorless forms. Zircon can be heat treated to produce the blue color found today. Red-brown colors are the most commonly found but zircon also comes is attractive shades of golden color, green, and red.