Opal has been a gemstone that lots of people love and some adore with a passion. I fit into the second category, probably because opal is about the only gemstone that can have such a diverse brilliance of colour that encompasses the whole of the colour spectrum. Because of this I find it such an uplifting and beautiful stone.
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.
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.
Check out the rest of the article here: http://www.crystalvine.co.uk/ethiopianopal.htm
Thanks again Sara for providing this article. I interviewed her next post, check it out!