Gemstone Dispersion

Dispersion is the display of color in a gemstone and may be classified as not observable, moderate, strong or very strong.

By Christopher Clark, GG, FGA, ASG, Gemologist & Co-Editor of The Sisk Gemology Reference | JTV
Published: 04/01/2020
Modified: 05/01/2021
gemstone-dispersion gemstone-fire
Gemstone Dispersion

Have you ever seen a rainbow when looking at a gemstone? This rainbow-like display of color is known as gemstone dispersion or as a gemstone's "fire." Gemstone fire, or dispersion, is the result of white light traveling through a gemstone at different speeds. The different wavelengths of light "disperse" when exiting the gemstone, creating the rainbow color display. Each gemstone has its own dispersion value; however the cut, size, body color and shape of the gem influence how well you can view the dispersion.

How can gemstone dispersion be classified?

A gemstone's dispersion may be classified as not observable, moderate, strong or very strong.

Dispersion in Gemstones (source: Gemstones.com YouTube)
  • A measured dispersion value less than 0.017 is classified as "not observable." Examples of gemstones with no observable dispersion are Quartz (0.013) and Glass (0.010).
  • Dispersion values ranging from 0.017 to 0.050 are classified as "moderate." Diamond (0.044) is a gemstone with a moderate dispersion value and is the gem most noted for its "fire."
  • Dispersion measured 0.051-0.071 is classified as "strong." Demantoid Garnet (0.057) is an example of a gem with strong dispersion.
  • Gemstone dispersion values greater than 0.071 are classified as "very strong." Synthetic Moissanite (0.104) has very strong dispersion.

How is gemstone dispersion measured and calculated?

The dispersion of a gemstone can be measured because gems have a refractive index (RI) for each wavelength of light. Gemologists use a refractometer to calculate the gemstone dispersion by taking the difference between the red (687 nanometers) and violet (430.0 nanometers) refractive indexes. This is expressed numerically with higher numerical values representing greater dispersion.

brilliant cut purple diamond gemstone
Purple Diamond

Both natural and synthetic gems can show dispersion, however it may be masked by the stone's body color if the saturation is moderate or stronger or if it has a dark tone.

Gems with higher refractive indexes tend to exhibit greater dispersion because they bend light to a greater degree. This happens when light travels through a transparent gemstone and it refracts or bends.

The spectral colors that make up white light travel at different speeds and when they bend, they begin to separate. Faceted gems are cut to reflect light internally as much as possible, before it exits the gem through the crown. The longer the light is refracting through the stone, the greater the separation of colors and the stronger the observed fire will be.

gemstone dispersion
Sphalerite Dispersion

Christopher Clark

About the author

Christopher Clark

A Graduate Gemologist and Fellow of the Gemological Association of Great Britain, Christopher has spent the last 4 years co-editing The Sisk Gemology Reference. He also acts as a customer advocate by inspecting and testing gemstones as they come into Jewelry Television to ensure they are exactly what our customers expect. He is an avid collector of vintage jewelry, gemstones, mineral specimens and spheres. Employed at Jewelry Television since 2006, Christopher spends much of his time immersed in the fascinating world of jewelry and gemstones.

Christopher’s passion for collecting valuables and precious stones began when he was shopping at a retired jeweler’s garage sale and he purchased a parcel of colored gemstones and a “lump of metal” that turned out to be GOLD! From that moment forward, the treasure hunt was on! But occasionally, he does become a commodities trader as he keeps an ever-watchful eye on precious metal prices. Unfortunately for his wallet, though, most of the treasures he acquires are never resold as they simply get added to his ever-growing collections. Christopher especially enjoys collecting vintage pocket watches and Mexican antique silver jewelry.

Christopher is now an Accredited Senior Gemologist with the Accredited Gemologists Association. He volunteers his time with a local gemological society for identifying gemstones. Christopher is always excited to attend major gemstone trade shows and is always on the look-out for the next great gem to bring JTV customers. Working closely with our vendors, Christopher has built a business rapport with them that allows for an easy trust and mutually beneficial working relationship. His favorite gem? Without a doubt, OPAL!