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Ethiopian Opal

Ethiopian opal is quite unique and different from more common Australian and Mexican opal.  Not many people know about this opal yet.  I am a gem cutter and have worked on this wonderful material quite a bit.  I want more people to know about this fascinating opal.  That is why I am writing this guide.

Brief History:

Ethiopian opal is, in a sense, an old gemstone.  In 1939, an anthropologist found evidence of use of the opal by early man in a cave in Kenya.  So there must have been an opal deposit somewhere in Africa.  Finally in the mid 1990s, the opal was re-discovered and a mineral engineer named Telahun Z. Yohannes started the mining.  The location is Yita Ridge, Shewa Province, Ethiopia.  I had a few chances to talk to Mr. Yohannes.

• Be cautious if an Ethiopian opal jewelry is advertised as an antique or vintage piece.  There is no such thing.  As of 2008, this opal has been on the market only for about 15 years. 
• As of December 2008, opal deposits have been found in Gonder Province and Welo (or Wollo) Province, Ethiopia. 
• As of October 2010, most opal roughs come from Welo Province.  The mining in Shewa seems declining.
• Lightning Ridge is located in Australia, and a production site of black opal, which is totally different from Ethiopian chocolate/black opal.   

The Roughs: 

The Yita Ridge roughs come in as small rhyolite geodes filled with opal.   Rhyolite is a form of granite.  Only about one percent of the mined geodes has opal with precious color play.  Some geodes are even empty, and most contain potch opal, which does not show color play at all.  Among the opals with color play, most are the dark brown, chocolate-colored variety.  The clear variety with color play is quite rare, but there are similar types in the Mexican opals.   The chocolate variety with color play is truely unique.

The roughs from Gonder and Welo come in without geodes and are more like Mexican fire opal roughs in shape.

• The varieties of opal base color include white, yellow, orange, dark red, root beer, caramel. chocolate and everything in between. 
• The degrees of transparency range from crystal clear to translucent to opaque, which no light passes through.

          

       Examples of base color and transparency of the roughs.  The two bottom left roughs are in the typical rhyolite geode.

• The varieties of precious color play include very unique Contra-Luz and patterns in broad flash, mosaic, snakeskin/leopard skin, stripes, pinfire etc. etc....
• The most common colors in the precious color play are red and green, but you see every hue in the rainbow in various shades, from delicate pastel colors to vivid electric colors to intense primary colors. 

In my opinion the most striking and distinctive of Ethiopian opal is the chocolate variety showing the colorful snakeskin pattern.  This pattern is also called the digit pattern, because the pattern also appears like fingers when the opal is sliced at right angles to the surface showing the snakeskin pattern.  But any variety with precious color play is absolutely breathtaking, and deserves to be called the queen of gemstones.  They can be cut into cabochons or faceted by an experienced cutter.

Chocolate opal rough from Shewa showing its color play in the snakeskin pattern.  In this stone the scale-like colors turn into stunning crimson red or electric blue with slight angle changes.

How to Examine Opal:

Precious opal with color play has numerous tiny silica spheres that are arranged in order in the structure.  You see the color play, when the light hits the spheres and is diffracted by them.  The broader the light spectrum is, the wider color range you see.  Since the sunlight is composed of the broadest spectrum of colors, the direct sunlight is the best light to inspect opal.  You can see the most colors an opal can show.  Examine the stone in sunlight rocking it back and forth from all sides.

About Contra-Luz Color Play:

Contra-Luz opal is unique in how it shows the color play.  It needs back illumination.  Contra-Luz (pronounce like KON-trah-LOOSE) means "against the light" in Spanish.   I am guessing that it is given a Spanish name because some Mexican opals show this color play and they have been mined before Ethiopian opals. 

I see this type of color play in the clear (or translucent) matreials from Shewa, but haven't seen it in the materials from Gonder and Welo. 

You can see the color best holding the stone up right in direct sunlight so the light hits its top or back.  But you do NOT look at the sun through the stone.  You cannot see the color that way.  The light must reach your eyes at angles, not straight through the stone.  The Contra-Luz colors appear as if they are suspended in the stone.  When you rock the stone slightly, different colors appear, i.e., play of color.  Illuminating the stone with a penlight closely from the side also works. 

To show the Contra-Luz color play, the light must travel within the stone.  The stone has to be transparent/clear to lightly translucent.  There is no opaque opal showing the Contra-Luz color play for the obvious reason.   

• I have seen a "Contra-Luz opal" listing showing the stone on a finger with the light coming from the above.  That is not the Contra-Luz color.  To show the Contra-Luz color, there should not be a thing (a hand, finger or table) directly behind the stone in the picture.   

   

This crystal opal rough is placed on a white paper with the sunlight coming from the above towards the paper.

 

This is the same rough with no frontal color play showing strong Contra-Luz color.  The sunlight is coming from the upper back. 

 

Faceted crystal opal showing the Contra-Luz color play.

A Note on Hydrophane/Cachalong Opal - An Oddity

There is an odd type of opal called Hydrophane (or Cachalong).  I have seen this type in Ethiopian material.  I think there is some confusion about its properties.  The followings are some comparison of what I have heard (information going around) and what I have seen myself (fact).  The pictures are an example.

• Ethiopian opal is mostly Hydrophane.
• I have seen a little in the material from Shewa and more in those from Gonder and Welo, Ethiopia.  The proportion of Hydrophane in the opal production seems various from locality to locality.

This is a colorful Hydrophane opal from Gonder, Ethiopia.

• Hydrophane means it does NOT become dehydrated.
• It does become dehydrated.  When it is dehydrated, the opal base is more opaque.  When it is hydrated, the base turns more transparent.  The transition time from the dehydrated state to the hydrated state, or vice versa, varies greatly from stone to stone (minutes to days).  This particular stone shows quick transition. 

The opal above is turning transparent from the rim in water.

This opal gets completely hydrated in 5 min.  It does not lose the fire.  The base returns white in a few hours, when out of water and wiped.

• Hydrophane is porous.  Dry Hydrophane absorbs water so avidly that it sticks to your tongue.
• It is true.  I have not tried it with my tongue, but it stuck to my wet finger.  I am sure it sticks to your tongue.  However, I do not think it is porous structurally like a sponge.  This water-absorption seems to occur at the molecular level.  Hydrophane opal is similar to silica gel, the desiccant. 

It stuck to my finger.

• It should NOT be soaked in water periodically.  OR on the contrary, I also have heard that it should be kept in water, because repeated drying and soaking causes the Hydrophane opal to crack.
• So far I have no problem with periodical soaking. 
• Most Ethiopian opals will temporary lose their fire when soaked in water.
• It does not lose the fire, when soaked.  See the pictures above. 
• I also have heard that a hydrophane opal loses its color, when it is dehydrated.
• It is possible.  If the color is the Contra-Luz type, it can be hard to see when the stone is dehydrated and turns opaque.

At least I can say that Hydrophane is a collector's opal due to its fascinating, peculiar nature.

Ethiopian Opal Buying Tips:

As same as you buy a gemstone at a store, your communication to the seller is a vital part of eBay shopping.  Ask them questions before committing to buy.  The honest sellers happily answer questions from buyers in a reasonable response time. 

Check their feedbacks carefully.  Walk away, if there is anything that makes you wonder or feel uncomfortable.  Most sellers are good and honest, but there are irresponsible sellers who sell low quality products or fake misrepresenting as something much more valuable. 

Now let us think about four Cs of opal. 

Color:

The color play is the most essential feature of opal.  Because the color play in opal is not still, it is tough to capture in photograph.  Considering all sorts of enhancement and touch-up softwares, be cautious about pictures that look unnatural.   

Clarity:

The clarity of crystal opal is graded like diamond such as VVS, VS, SI, I and so on.  Both SOLID inclusions and CRACKS are called inclusions, or some say, flaws or flawlines.  The chocolate variety is opaque and cannot be graded in a conventional way. 

Whichever the variety you are interested, by all means, choose a stone free of cracks for beauty and strength.  A few solid inclusions are common in crystal opal and acceptable.  Pay attention to any irregular lines that appear ON and IN the stone in the pictures.  Those are usually fracture lines.  If once a stone starts cracking, the cracks tend to run weakening the stone.  If I have to pick a fractured stone, I prefer an Opticon-treated stone to untreated one. 

• About Opticon:  Opticon is an epoxy resin.  It is also called fracture sealer, fracture filler, stabilizer etc.  It fills in surface-reaching fractures in the liquid state, and later solidifies with the hardener.  It is NOT a glossy coating like a nail polish.  It does not enhance or alter gem color.  The treatment is permanent.  Because it is a form of treatment, some people are against using it.  But with the disclosure, I am for it on stones with minor fractures.  There are so many beautiful stones worth being admired this way rather than tossed without the treatment.  That being said, the Opticon treatment on opal is still controversial, because Opticon, which is colorless amd clear initially, turns yellowish over years.  I would recommend it only as the last resort.

Carat Weight and Cut:

Opal is a light stone.  In other words, a 1-carat round brilliant-cut opal is larger than a 1-carat round brilliant-cut diamond (approx. 7.5 mm vs. 6.5 mm).  You need to know the exact size of a stone, if the stone will be used in a piece of jewelry. The quality of cut and polish is also important.  Ask the seller untill you are sure how big and what cut quality the stone is.

To find a high quality stone, don't fall in love with the first stone you see.  Look around and compare stones.  Pay attention to the details.  You will see the difference. 

• For more information on a well-cut stone, click to take a look at my another guide: How to Find Precision-Cut Gemstones on eBay

Making an opal gemstone involves purchasing the rough and cutting/faceting the rough into the gemstone.  It takes hours, sometimes days.  Quality comes with value.  I believe you should pay for the quality.   Depending on the quality, the price may be lower or higher.  You can get many junks for the price of one good gem.  By the way, this applies to any other gemstones. 

Opal Care:

I recommend soaking solid opal in plain water for a short time occasionally, say, an hour every month.  Water is one of the chemical components that make up opal.  Opal's mineral/chemical name is hydrated silicon dioxide.  Its structure is more like hard jello rather than sponge soaked up with water.  Opals gradually lose the water under dry conditions and start to crack.  It is called crazing.  Never put opal in oil or in detergent solution, because it may lose the color.  Dirt can be removed by wiping with a tissue paper moistened with rubbing alcohol.  Opal should never be heated.

• If an opal is soaked in water too long, e.g. for days, there is a small chance that the opal fractures internally after it is taken out of water and dried.  I have gotten a couple of fractured opal this way.  My guess is when the opal gets too much water, parts of the stone expand unevenly, and this stress causes cracks.  Or those internal fractures have been there, but get more visible due to the uneven expansion.  
• Australian doublet and triplet opals should not be soaked in water, because they are glued together with other materials.