For generations, Australian opals have been the most popular, nearly the only, opals in jewelry. However, with the 2008 discovery of stunning, fire-filled opals in the Wollo Province of Ethiopia, Australian opals are going to have to learn to share the spotlight.
Ethiopian opals can contain vibrancy and color to rival or best Australia’s finest, and the stones frequently display beautiful patterns completely unique to the region. Opals from Wollo Province are also sturdier than the notoriously delicate Australian stones, able to withstand stronger impacts without cracking. These amazing gems have rocketed in popularity since their arrival on the international market, and can be expected to continue doing so as new deposits are found. (See: Rondeau, et. al. “Play-of-Color Opal From Wegel Tena, Wollo Province, Ethiopia.” Gems & Gemology 46.2 (2010))
Opals are relatively soft compared to many gemstones. As such, they can be scratched, and if dropped or struck they may crack or shatter. Ethiopian opals are stronger Australian opals, but should still be treated with care. They should not be allowed to dry out, which can happen in places deliberately kept at low humidity, such as bank vaults, or when kept under bright hot lights for long periods. Opals are vulnerable to extreme heat and very vulnerable to acid. When opals are set in a doublet or triplet form, care must also be taken regarding the adhesives involved, which may not respond well to extended soaking, or solvents.
Ethiopian opals are usually hydrophane opals, which means they have the ability to absorb water. Special care should be taken with hydrophane opals to avoid strong chemicals, as they may make their way into the stone. If your Ethiopian opal is exposed to water for a long period of time, you may see it start to lose color. If the opal is taken out of the water it will eventually return to its original state. This dehydrating period may take a few hours or a few weeks, depending on the humidity in the air, but the stone will eventually return to its original state. There is some concern that if an Ethiopian opal absorbs a great deal of water it could result in cracking. We at Hidden Fire Gems have not personally seen this phenomenon, but still encourage people to be wary of soaking their stones for extended periods.
Ethiopian opals that are newly mined are known to sometimes crack, craze, or change color once exposed to the atmosphere. All Ethiopian opals sold by Hidden Fire Gems have been out of the ground for over two years, and should not be at risk for any of these changes if treated with reasonable care.
When these opals were paired to make earrings, they were matched in color. However, over time the left stone took on a yellow tint, the right remained white.
The language used to describe opals has not been formally codified. Different people may use the same term to mean different things. We at Hidden Fire Gems try to use terms in a way that both appear logical to us and are supported by many in the industry. However, we understand that there are others who have different definitions.
Opals are made of water and silica, in the form of hydrated silicon dioxide. Opals can contain from 3% to 20% water. The structure of opal is amorphous, rather than crystalline. Opal is formed when water seeps through stone, picking up particles of silica, and then flows into voids in the stone. Because of this, one can sometimes find opalized fossils, created when opal filled the space left as the original organic material decayed.
An opalized fossil from Australia
Types of Opal
Common Opal - Most opal in the world is common opal. Common opal may have a milky or pearly luster known as opalescence, but lacks the brilliant flashes of color from within (play-of-color, or fire) that are associated with Australian or Ethiopian opal. Examples of common opal that are still appreciated for their beauty are Peruvian opal, and most Mexican fire opal.
Blue Peruvian common opal
Precious Opal - this type of opal has minute uniform spheres of silica arranged in a three-dimensional grid, which diffract light, producing flashes of color when viewed from different angles. This phenomenon is known as play-of-color, or sometimes fire (not to be confused with fire opals). The desirability of precious opal is based on the intensity, diversity, pattern, and angles of visibility of the play-of-color.
An Ethiopian precious opal full of play-of-color
Fire Opal - A transparent to translucent opal with a body color that is orange, red, or yellow. Most do not have play-of-color, meaning they are not “precious” opal. Fire opal that does display play-of-color, or internal fire, is classified as precious fire opal. Mexican fire opals are known particularly for their rich color.
Some of the range of color to be found in Mexican fire opal.
Honey Opal - Ethiopian opals in shades of yellow and orange are generally referred to as "honey," not fire, likely because they tend to have a more organic-looking caramel coloring.
A selection of honey Ethiopian opals, with red and green play-of-color
Boulder Opal - This opal is displayed within the host rock. The contrast between the opal and the surrounding rock often causes the play-of-color in the opal to be more noticeable. This setting calls attention to the geological origin of the stone, making it educational as well as visually appealing. Mexican fire opals often occur in a pink host rock, creating particularly lovely and unusual boulder opals.
An Ethiopian boulder opal and a Mexican boulder opal
Matrix Opal - The opal is mixed intimately with the parent rock, appearing in flecks and flashes of color throughout the stone. Fairy opal, Andamooka matrix opal, and Honduran black opal are all examples of matrix opal.
Doublets and Triplets - These are assembled stones. Doublets are stones where opal has been layered over another, darker, stone, to make the fire more visible. Triplets also have a clear cap added above the opal, which both protects the stone and enhances visibility.
Australian Opal doublets
Ethiopian Opal - Sometimes also known as Welo or Wollo opal from the name of the province of Ethiopia where most opal is currently mined. Opal was first discovered in Ethiopia around 1993, in Shewa Province. The opal from those mines was especially delicate and given to cracking, as well as being of less popular colors, and was not considered commercially viable. In 2008 opals were discovered in the Wollo or Welo province. These opals proved to be more robust than opals from Shewa Province, or even traditional Australian opals. They also displayed beautiful color (primarily white or honey) and unique patterns, becoming the basis for the current Ethiopian opal phenomenon. A later mine discovered in 2013 in a different part of the province has produced predominantly dark and black body color opals. Ethiopian opals are mostly hydrophane, meaning that they absorb water upon immersion. As the stone absorbs water, it will become clear. If removed from the water, the stone will eventually return to its original state.
An Ethiopian opal before and after soaking in water
Australian Opal - Australian opal was first discovered in the mid-1800s, and has been the predominant precious opal on the market since then, to the point where, for many people, “opal” without any modifier is always assumed to mean “Australian opal.”
A freeform carved Australian opal
Mexican Fire Opal - Mexico is the world’s primary source for fire opals. Mexican fire opals are known particularly for their rich reds and oranges. They may or may not have play-of-color. Unlike many opals, this stone is usually faceted to add the element of sparkle. Mexican fire opals often occur in a pink host rock, creating particularly lovely and unusual boulder opals. Not all Mexican opals are fire opals; Mexico produces some colorless, crystal-clear opals that nonetheless can be filled with precious play-of-color.
Two Mexican opals, one orange fire opal, and one white, both with play of color
Fairy Opal - A form of matrix opal, which may also be known as carbonized sandstone matrix, opalized sandstone, concrete opal, rainbow matrix, rainbow opal matrix, or mass opal. These stones are composed of Australian sandstone that has been impregnated naturally with opal. In its raw form, the color is very difficult to see against the pale sandstone body of the stone. Fairy opal is treated by carbonizing, which can be done by cooking in sugar or soaking in oil and heating to turn the base stone black, and impregnating with resin to stabilize the fragile sandstone so it can be polished. Other matrix opals, which are very visually similar, include Andamooka matrix opal, which has a base of limestone instead of sandstone, and Honduran black opal, which is not color treated as the natural host stone, basalt, is already dark.
An Australian Fairy Opal
Opals can display fascinating patterns within their coloring, and Ethiopian opals are even more likely to have patterning than opals from other locations. Some examples are:
Pinfire - Dense pinpoints of play-of-color are visible throughout the stone.
Harlequin - This pattern consists of broad, angular, closely set patches of color.
Patch - Clear patches of play-of-color are visible in the stone, but with space between them, not placed as densely as with harlequin.
This opal displays patch patterning, with a bit of pinfire in the center.
Digits - Ethiopian Opals are particularly known for digit patterning, and its associated pattern, honeycomb. This pattern is based in columns of opal in the stone, separated by a matrix of a visually distinct type of opal. When viewed in parallel to these columns, they look like fingers extending into the stone.
Honeycomb and Fishscale - When digit patterning is viewed from perpendicular to the columns the pattern will appear like a series of cells separated from each other, like the cells in a honeycomb. When the matrix separating the digits from each other is not clearly visible, the pattern looks more like the scales of a fish than the cells of a honeycomb.
Rolling Fire - This is when the play-of-color appears to move across the surface of the stone as the viewing angle changes, rather than simply flashing on and off.
These are only some of the patterns appearing in opals that have been given names, and we can expect that the list will expand as more people become familiar with Ethiopian opals.
The way that Ethiopian Opals absorb water makes them ideal candidates for dyeing, sugaring, smoking, and other treatments. We at Hidden Fire Gems will never knowingly sell a treated opal without disclosing that it has been altered, but though we do our best to sort out any such stones, we are limited by the equipment we have access to. We are willing to provide a formal Gemological Institute of America lab report on the condition of our higher-end stones.
All images are copyright Hidden Fire Gems, and are of opals in the Hidden Fire Gems stock.
For further information please see articles from Gems & Gemology, https://www.gia.edu/gems-gemology, particularly: Rondeau, et. al. “Play-of-Color Opal From Wegel Tena, Wollo Province, Ethiopia.” Gems & Gemology 46.2 (Summer 2010), Kiefert, et. al. “New Deposit of Black Opal from Ethiopia.” Gems & Gemology 50.4 (Winter 2014) and websites such as https://www.gia.edu/opal, http://geology.com/gemstones/opal/, http://www.johnosopals.com/2010/11/treating-andamooka-matrix-opal and of course, https://en.wikipedia.org/wiki/Opal