A translucent to transparent opal with a wonderful fire-like background color of yellow, orange, or red.
Author: Hobart M. King, Ph.D., GIA Graduate Gemologist
What is Fire Opal?
"Fire Opal" is a term used for colorful, transparent to translucent opal with a background color that is a fire-like hue of yellow to orange to red. It might or might not exhibit "play-of-color" (the typical flashes of spectral colors that can be seen when a precious opal is turned under a source of light). Most fire opal does not have play-of-color. The defining characteristic of fire opal is the fiery hue of yellow, orange or red that serves as a uniform background color throughout the stone. These colors are thought to be caused by the presence of small amounts of iron in the opal.
The value of a fire opal is based upon the desirability and uniformity of its color, with yellow being on the low end of value and red being on the high end. Transparent stones are preferred over translucent stones. The best fire opal typically sells for prices that are much lower than the best precious opal; however, fire opal specimens with exceptional color will sell for higher prices than some specimens of precious opal with less impressive play-of-color.
"The defining characteristic of fire opal is the fiery hue of yellow, orange, or red that serves as a uniform background color throughout the stone."
How are Fire Opals Cut?
Fire opals are cut in a variety of ways. Some are cut as faceted stones, others are cut as cabochons. The cutter decides how he/she thinks the stone will be most attractive. There is no rule for cutting fire opal.
Transparent fire opals are often faceted so that they can be illuminated by incident light. If they have a spectacular play-of-color, they might be cut into a cabochon like most precious opal. If the play of color is minor, it might be cut into a faceted stone with a little surprise of flash.
Translucent stones are often cut into cabochons, but it is not unusual to see a translucent to nearly opaque fire opal with an attractive color cut into a pretty faceted stone. The three stones in the photo at the top are wonderful examples of translucent stones that have been faceted.
Durability of Fire Opal
Fire opal has a Mohs hardness of 5.5 to 6, which is soft enough that it can be scratched by many objects that it might encounter if set into a ring without a setting especially designed to protect it. Fire opal also has a low tenacity, which means that it can easily be chipped or broken. So, fire opal is best used in jewelry such as earrings, pins, and pendants that usually are not subjected to rough wear.
Public Confusion with the Term "Fire Opal"
There is some public confusion with the material known as "fire opal" and the gemstone phenomena known as "fire" and "play-of-color." What do the terms "fire" and "play-of-color" mean?
"Fire" is a name used for flashes of spectral colors that are produced by the dispersion of light into its component colors as it passes through a transparent material. Most people are familiar with how a prism splits white light into a spectrum of its component colors. That phenomenon is known as "dispersion." Diamonds are famous for their colorful sparkle of light known as "fire" which is also caused by dispersion. Fire opal does not exhibit dispersion, thus it does not have "fire" like a diamond.
"Play-of-Color" is a name used for the flashes of spectral colors that are produced by "precious opal." Those colors are produced when light is scattered by an array of microscopic silica spheres that are stacked to make up the color-producing parts of a precious opal. The technical name of this light scattering is "diffraction."
This same type of color is produced when droplets of water in Earth's atmosphere interact with sunlight to produce a rainbow. The rainbow colors of iris agate are also produced by diffraction.
Fire opal will occasionally exhibit "play-of-color." When it does, some people call it "precious fire opal." A photo of "precious fire opal" can be seen on this page.
What is "Fire Opal"?
Fire opal is the name used for a colorful material with a limited range of background colors. It is not a name given because of a phenomenon. It is an opal with an attractive background color that ranges from yellow to orange to red. The attractive background color is what defines the stone.
Fire Opal Localities
Mexico has been the world's primary source of fire opal for decades. The Mexican deposits produce significant amounts of transparent to translucent, bright orange to orange-red material. Some of the transparent material is faceted, mounted in commercial jewelry, and described as "tangerine opal" because of its color. Smaller amounts of fire opal are produced in Australia, Brazil, Ethiopia, Honduras, Guatemala, Nevada, and Oregon.
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