Imperial Opal - Opale Imperiale

Ethiopian Imperial Opal

Constellations of Colour - Queen of the Queen of Gemstones, the EMPRESS of Precious Stones.

"Opale Impériale" Français

In 2008 in the high arid mountains of Wollo (Welo) province of Ethiopia a "new" volcanic origin Opal CT (Cristobalite-Tridymite) was discovered. The finest examples of this gemstone are called IMPERIAL OPAL and may be faceted as well as cut in the usual cabochon. They are easily the most rare and most beautiful of precious stones known. Pliny the ancient Roman once called Opal the Queen of gems: Imperial Opal is thus the Empress of Precious Stones. J.D.Sage (Troubadour)

Photography & Comments by Gemologist Gregory Kratch to the Lapidary Journal Editors 2013

The GemGuide

Article by Gemologist Gregory Kratch

Ethiopian Opal

For nearly a decade now, the new find of opal in Ethiopia has been both welcomed and debated on issues of stability and high water content. Some of the material can be quite beautiful and with the quantity that is now available, we need to understand how to handle it better.

The recent discoveries of opal in Ethiopia, and in particular the finds at Wegel Tena in 2008 have had a profound effect on the world opal market. Opal is now more popular than ever. With its astounding brightness, remarkable new patterns, and unusual physical properties, this opal is quite different than the Australian opal which has been the market standard until now. Unlike the most Australian opal that comes from sedimentary deposits, the new opal from Ethiopia is mainly formed in a volcanic environment. Ethiopian opal is classified as opal-CT. This type of opal is composed of lepisheres or small balls of crystals of quartz group crystals, tridymite and cristobalite, which are polymorphs of SiO2, produced under high temperature and pressure. Australian opal is classified as amorphous (opal-A).

Ethiopian opal from Wegel Tena is a hydrophane, but very different from the hydrophane opal of Australia. Hydrophane opal is porous, and can absorb water. When Australian hydrophane opal is soaked in water, it will absorb some and show a play of color (often spectacular) that slowly dims or disappears when the stone is removed from the water and dries out. Because Australian hydrophanes only show their best play of color when wet, they are therefore not suitable for jewelry. However, the Ethiopian hydrophane opals show their best play of color when dry, becoming more transparent and less colorful when immersed in water. Once removed from the water, they will at first become very cloudy to opaque, and then gradually return to their original state over a period of a few hours to several days as they dry out. Stones should not be heated or treated chemically to speed up this process. This capacity to absorb water and release it with no damage to the stone is remarkable. Specimens I have tested have varied widely in their ability to absorb water with stones ranging from 4% to 15%, based on the dry weight. A gain of 20% was reported by one dealer. Therefore, I recommend that all opal be correctly identified at the time of sale so that the owner may properly care for it, and keep it at its best and most beautiful. The CT hydrophane opals are very different in many unique ways from what we have predominately seen in the world market to date and must be cared for accordingly.


Fig. 1. These two opal rough specimens are from Wollo. While the rough on the left is spectacular for the pattern and spectrum, the rough on the right shows another side to the field's potential—natural dark opal form Wollo.Courtesy of Francesco Mazzero/Opalinda.

Stability is always a concern with any opal, especially with new sources if they have little history. Although Wegel Tena seemed to offer a new supply of stable opal, there have been incidents of instability, cracking and crazing. It is imperative to remember however, that all opal fields produce opal that is unstable. Hungary, Australia, Mexico and Brazil have all produced their fair share of unstable material, some of which unfortunately entered the market. Ethiopia is a whole new frontier. We will be better able to predict its stability, as we explore and discover this new source of gem opal. I have found that once stones were cut, very few have developed any problem. Similar experiences are shared by other experienced cutters. As the opal industry grows in Ethiopia, I am sure it will develop the same checks and balances within the industry itself of reputable miners, dealers and cutters that hopefully will help keep unsuitable material out of the trade. No one wants to sell bad opal; it is not good for your reputation or the industry. It would be prudent to buy from people who have a longstanding reputation with opal in the current market and who you can easily contact if any unexpected problems develop with your stone. Some dealers may even offer time limited guarantees of up to six months for unset stones. Discuss any concerns you may have with your vendor at the time of purchase. Everyone wants a happy customer.

This new opal from Wegel Tena is also exhibiting some characteristics that are quite different and unique. Rondeau et. al. published a detailed study of Wegel Tena opal in Gems and Gemology Summer 2010. Cut opals from Mezzezo, Ethiopia and Australia (including a piece of boulder opal) as well as Wegel Tena were dropped on a concrete surface from a height of 1.5 meters. The stones from Wegel Tena showed no damage even under the microscope. All the other samples showed breakage. Its unusual durability makes it a great candidate for faceting, creating stones with kaleidoscopic constellations of color, a whole new avenue to explore. In a different experiment by Stone Group Laboratories, selected material from Wegel Tena was subjected to smoke treatment to darken the stones, with an astonishing survival rate of 90% despite the high heat and extreme dryness. The physical structure and hydrophanous nature of the treated stones, among other things, differentiate them from natural black Australian opal. Although they are attractive, they can never rival the finest blacks of Lightning Ridge. This remarkable new opal, is quite unlike the others in many ways. It should be treated, handled and stored differently as well. I am sure that these new fields of opal in Ethiopia have many wonderful surprises in store, and we should welcome this new imperial addition to the court of the queen of gem; opal. “…which contains the fire of the carbuncle, the glorious purple of amethyst, and the sea green of emerald all shining together in incredible union.” Historia Naturalis, Vol 37. Pliny, 23-79 AD

Gregory Kratch is a miner, gemologist, lapidarist, opal expert and cutter, and a frequent lecturer at the Ecole de Gemmologie de Montreal.

Dear Sirs,

You published an article in the Lapidary Journal January/February 2012, on the "new" Ethiopian Opal. As I have been cutting this material for years, I wanted to add some of my own observations and experience with this beautiful and very important new discovery, particularly the opal from Wollo Province. As your article correctly noted, this opal is a Hydrophane Opal formed in a volcanic environment. But the differences in formation and physical structure mean that it is not always comparable to opal formed in a sedimentary manner, as is most of the Australian opal. The descriptions in your article of hydrophane and its reaction to light and production of colour in a dry and wet state I consider incomplete in some very important aspects. While it is true that almost all hydrophanous opal will show brighter plays of colour while wet, upon drying, the sedimentary hydrophanes tend to become duller and duller as they dry and the water leaves the stone, their highly porous and irregular structure continuing to interfere with the transmission of the light and consequent production of a play of colour, until the opal may appear almost opaque with virtually no discernable colour.

Unfortunately the article failed to mention that when the opal from Welo (Wollo Province) begins to lose its water content it becomes more opaque or creamy at first, and then begins to clear over a period of a couple days or weeks, if left in a normal environment in a room at normal temperature as the stone continues to dry out. I would not recommend any forced heat to speed up the drying process. Each stone is different. In this way it is similar to the chameleon opal from Java, also formed in a volcanic environment. The Javanese opal also shows its best colour play when it dries out, unlike most opal from sedimentary deposits that look better when wet. And often, even usually, the new material from Wello is more beautiful dry than wet. In the finer near transparent grades I find the slight cloudiness or turbidity in the cut stones, a slight haziness in an almost transparent base, a slight translucence makes them more beautiful and can show more colour than when fully hydrated and completely transparent. It is similar to what happens when you cut a cabochon of very clear crystal opal and put a very high polish on the back of the stone, the highly polished surface allows the light to leave or leak out of the back of the stone with very little light returned to the viewer except the play of colour. However, a soft even slightly frosted finish on the back like a satin 600 surface, scatters some light and lights up the stone better often giving a better more perceptible colour play. In the best Ethiopian material, in my experience, the stones are actually more beautiful when completely dry with a slight haziness to scatter and spread the light around. The entire stone lights up better. Lower and lowest grades, less transparent or opaque opal may be much better when wet. I have limited experience with material of this lower quality. As always with opal, it depends on the individual stone. They are all different, and that's the charm. Often frustrating, but always interesting. The article failed to mention that this new hydrophane opal from Welo would not react like most others, Java excepted, and after an initial period of dulling, when first removed from water and begins to dry out, would then continue to become more transparent and show a better and better colour play as the dehydration continues.

There were other issues I would like to discuss concerning the description of blacks (I have seen a few as well as some beautiful crystal opal on a natural black skin, sort of like a colour bar over a thin black base as seen for example, in some boulder opal, but probably with an iron and manganese oxide crust in the case of the Ethiopian opal from Welo). And base colour and temperature sensitivity as well as iron content and stability are a whole other discussion. I felt it important to write you about the impression your article left that all hydrophanes are only beautiful when wet and lose their colour when dry. This is certainly not the case with the material from Wollo Province.

With the continuing reduction in production of the Australian fields, this new discovery of opal, and in particular, the new opal from Welo, is rapidly gaining acceptance and market share because of it's pure colour and astoundingly bright colour play, exceptional and unique patterns, and just sheer beauty. The Troubadour and Poet J.D.Sage* has dubbed it “IMPERIAL OPAL” the Empress of precious stones. I concur. We should thus enthusiastically welcome this lovely new addition to the royal family of gem opal, the new Ethiopian Imperial Opal, truly an Empress in this family of the Queen of Gems, as Pliny the ancient Roman so aptly described opal, so long ago.

Gregory Kratch
Gemologist

Please follow links to learn more about Imperial Opal (Ethiopia). http://www.jtv.com/library/ethiopian-opal-gia.html
http://www.jtv.com/library/Ethiopian-Opal.html
https://www.youtube.com/watch?v=uFtesRTeBCk

帝后欧珀

J.D.SAGE Troubadour
Imperial Opal (Instrumental)