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GemSelect | Gemstone Fire and Dispersion

What exactly is gemstone fire you ask?

Well, some gemstones will display flashes of color, resulting from the dispersion of white light into colors.

Diamond is very well famed for its fire, but unknown to many, a number of other gemstones are very notable for their fire as well, including demantoid garnet, sphene and zircon.

However, there is a very special gem which has even greater fire and it is unknown to most. In fact, this gem has a dispersion rating three times higher than that of diamond! This amazing gem is called sphalerite.....

Watch the Video and Witness the Fire!

GemSelect Sphalerite Gemstone from GemSelect on Vimeo.

The term "fire" in gemology, refers to the ability to split light into the colors of the spectrum. The term "scintillation", also in gemology, refers to flashes of light produced when a gem is moved in light.

Many gemstones are cut and polished in a manner featuring series of planar surfaces known as facets. The facets on the top of the gem, known as the crown, have the function of capturing light. The facets on the bottom of the stone, or the pavilion, are responsible for reflecting the light internally. This systematic process of capturing and reflecting light produces several different illuminating optical effects. In this article, we consider the optical illumination effects of fire and scintillation. We suggest reading our other articles to learn more about brilliance and luster.

As previously noted, fire refers to a gem’s ability to split light into the colors of the spectrum. The technical term used in gemology is dispersion. This phenomenal act of dispersion occurs when different light frequencies are refracted to different degrees by the refracting medium. Diamond is the most famous gemstone known for its dispersion, but several other colored gems are also notable for their impressive dispersion, sphene, demantoid garnet and zircon.

Gemologists measure a gem’s dispersion using a refractrometer. The dispersion rating is usually a numerical figure that represents the difference between violet and red refractive indices. However, it is not advisable to rely entirely on the numerical dispersion rate when it comes to predicting how much fire a gem will exhibit. Darker gemstones tend to exhibit less fire compared to lighter colored gems, and cleaner stones will also exhibit more fire than gems with many inclusions.

Scintillation refers to flashes of light produced when a gemstone is moved in light. The effect of scintillation is a result of alternating displays of reflection from polished facets of a gem. The reflections may be white or other various colors and very often they are similar tones, but brighter than the actual body tone of the gem. A blue sapphire may flash bright blue hues, but red spinel may flash bright red or even orange hues. Sometimes these flashes show a secondary hue, such as amethyst, which shows red flashes and spessartite garnet, which flashes orange and yellow.

In the gem business, here in Chanthaburi, we often overhear dealers referring to scintillation as "fire", but this usage is not really gem-o-logically correct, although it is understandable to confuse the terms. Bright flashes generated from the facets of a well-cut gem, do indeed look like fire, in gemology, fire pertains to the splitting of light into the spectral colors, which is sort of like a multi-colored scintillation.
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