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.
To see more opals clickon 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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