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In the past most opal has come from either Australia or Mexico, as opal mainly comes from two types of deposits; volcanic and sedimentary. Australia provides the largest sedimentary deposit, whilst Mexico the largest siliceous volcanic deposit. Smaller deposits can also be found at opal Butte, Oregon, although this mainly is not commercially exploited for jewellery.
However, as late as 1939 the famous anthropologist Dr. L. Leakey reported that early man used opal to fashion tools based on a discovery of artifacts in a cave in Kenya that were dated from around 4,000 years B.C. and so believed that opal mines must exist in Africa. In was not until much later in 1994 that actual proof of these opals came to light with a Dr. N. Barot who reported in an article in the ICA Gazette that opals from Ethiopia had been seen at a Nairobi gem market in 1993. In the same year a minerals engineer by the name of Telahun Yohannes learned about these opals whilst on holiday and started investigating its location along with a lease to explore and mine the area. And that begins the start of a new and stunningly beautiful opal onto the market.
These opals are found at Yita Ridge, in the Menz Gishe District of Shewa Province, around 150 miles northeast of Addis Ababa, the capital of Ethiopia. The opal field lies around 12 miles north of Mezezo and extends for several square kilometers along the northern side of the Yita Ridge.
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| Map courtesy of Gems & Gemmology magazine. |
Map modified from Ethiopian Tourist Commission map 1992 |
The opals are found in a nodular form within a continuous layer of welded volcanic ash (tuff, similar to obsidian in character), about 3 metres thick, that lies between weathered rhyolite layers. The nodules are very numerous though in my opinion the percentage of gem precious opal is quite small. In 1997 out of 10 kilos of un-opened nodules I acquired I found only one with good precious opal, around 20 with some colour play and the rest were either empty, filled with common opal or quartz. Figures in 1995 estimated that around 15% of the opal recovered was gem quality, and around 1% shows distinct play of colour.
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| Empty Nodule |
Common Opal |
Good Ethiopian opals are quite diverse and ever since I first acquired them have shown a variety of base colours, including red, orange, clear, white, grey, black, yellow, blue, brown and green. The play of colour shows in the usual way or as a contra-luz, when held against a light. The best pieces show vivid play of colour usually with the full colour spectrum as well as turquoises and indigos, as seen below. These two opals have been around the most unusual and beautiful that I have obtained from this region. The second example did not show any evidence of the usual rhyolite matrix around it.
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| Photography by Crystal Vine |
Photography by Crystal Vine |
More common are the nodules with a brown or red base colour like the examples below.
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| Photography by Crystal Vine |
Photography by Crystal Vine |
In some cases I have actually found nodules that have two different base colours with each showing play of colour, or areas that show colour and areas that do not, as the example below shows.
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| Photography by Crystal Vine |
You can see from the photos that this material can be polished. However it should be noted that a lot of the opals do in fact show internal fractures and crazing that in my opinion do not detract from their beauty. In fact I wear a polished slice showing fractures which I made into a pendant, and it is always admired. I also have some opals that have been cut and show no fractures at all.
It is still relatively early days in the exploration of these opals and cutters are finding new techniques and ways to bring these beautiful opals to the market. The photographs will never do these opals justice, so if you are interested you need to find the real things to discover just how amazing they are.
07/03/09
Last year some Ethiopian opal started to hit the market which appears a lot different from the material from the Yita Ridge. This new material appears to be coming from the Afar Region which is an ajoining area to Addis Ababa. I have several opals from this area for sale in my Opal gallery as they are quite stunning.
Here are 2 examples. You can see that there is hardly any matrix and in some cases there is just a very soft earth so the opals are principally without matrix. I have also found some strange things happening when I have polished some of these pieces. An example is below.
Belive it or not these are photos of the exact same Ethiopian opal. I started off with a lovely clear opal that had very nice colour play with an orangish background and polished one side, leaving the back natural, like below.
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I left the opal overnight before I started to add them to my opal gallery and noticed that a change was taking place, in that the opal had started to become cloudier. I left it in my pocket to pick up some warmth and within hours the opal had turned completely opaque and was now showing a white background. I have had strange things happen before with Ethiopian opal where the colour changes as I am polishing it, but as soon as it dries the colour reverts back to it's original colour. This is the first time that I have witnessed something so dramatic. I suspect that if I cover it in water the colour might go back to being clear again, but this I think would only put stress on the opal, as drying out and being immersed in water many times expands and contracts it. More examples of this new material can be seen in my Showcase gallery.
In this new material I have also come across specimens where there is an opal within an opal. Below is an example where the actual colour play is solely within the inside opal. You can clearly see the inside bubble of opal within a clear opal nodule. These are very strange and maybe have formed in the same way where you find a manifestation quartz, a quartz crystal within a quartz crystal.
To see more opals click on the link to our Showcase Gallery or visit our shop where you will find a range of opals for sale.
References
Gems & Gemmology magazine Summer 1996 Lapidary Journal, July 1996
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