Ethiopian opal on auction at http://www.opalauctions.com.
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WELO Rough 32.83cts Red Blue Yellow & Green Fire! A923 kilnbrookopals |
100.00 | - | 32.83 | 17 hours 50 minutes |
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HUGE Pear HIGH DOME WELO 5.43 cts.16×13x6 mm RED Butterfly opalfireinfo |
500.00 | - | - | 17 hours 50 minutes |
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ETHIOPIAN WELO OPAL~BRILLIANT CABOCHON~2.7ct TopShelfOpals |
549.00 | - | 2.7 | 18 hours 50 minutes |
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AAA GONDOR DESERT ETHIOPIAN OPAL 1.65 CTS NC-311 NiceOpals |
55.00 | - | 1.65 | 18 hours 50 minutes |
How was opal formed? Scientists have a variety of theories.
Here’s the facts, as far as Australia’s opals were formed:
The Great Artesian Basin is a stretch of Australia that covers about half of the eastern half of Australia, mostly in Queensland, but with the famous Coober Pedy and Andamooka fields in South Australia, and Lightning ridge in the north of New South Wales.
This geographical feature was formed during the Jurassic and Cretaceous periods, betwee 200 million to 70 million years ago. For much of this time, this part of what would become Australia was a shallow, inland sea. As with any sea, sandy sediments, and sandy clay sediments, settled out of the water.
Then, 37 to 70 million years ago (the Tertiary period), the earth’s climate changed. (Perhaps caused by a bit of non-manmade global warming.) The sea receded, and what was left behind was millions of years of history. The sediments were now over a hundred feet thick, layers of gray shale, shaley mudstone, limestone, and sandstone.
Most scientists theorize that most of Australia’s opal was formed after the Cretaceous sediments began to weather, which freed the silica trapped within. This silica then would dissove during rainstorms, trickle through faults in the subsoil, and become trapped within wood, shell, bone (thus “opalizing” these items), or would simply become trapped in cavities in the subsoil. The water would evaporate, the silica would remain, and become concentrated to such an extent that they would form microscopic spheres.
In 1921, the Mintabie opal field was found. Opal historian Fred Ward calls it “strangely beautiful…with its full range of black dark and light opal.
Andamooka, the last major opal field to be found, was open in 1930.
Mintabie, Coober Pedy and Andamooka opal fields are located in South Australia. Lightning Ridge and White Cliffs opal fiels are found in New South Wales, and in Queensland, there are the Opalton, Quilpie, Koroit and Yowah fields.
The opal mines in what is now Hungary supplied Europe with opal. One of these was a stone for the crown of a Holy Roman emperor. Despite the popularity of opal, some writers (who of necessity would be religious – only the clergy were literate) associated opal with bad luck.
Another famous mention of opal takes place in Sir Walter Scott’s novel, Anne of Geierstein (1829), which also comments that opal is bad luck. Experts say that it was after the publication of this novel that the popularity of opal plummetted.
However, by the 1890s, opal had regained its popularity.
This was spurred in part because Queen Victoria of England loved opals, and wore several necklaces. In addition, vast opal deposits were found in Australia, and with such a large supply of the beautiful gem, its popularity restablished itself.
Opal Discovery in Australia
The opal that was imported into Europe from the Hungarian mines were usually white, with little play of color. The discoveries of opal inb Australia changed all this. They were large, they were brilliant, and the play of color was spectacular.
In 1849, white common opal was found South Australia. Fourteen years later, in 1863, opal with play-of-color was found. Then it was found in Queensland.
In 1890, Australia’s first commercial opal mine exported light opal from White Cliffs in New South Wales.
In 1903, black opal from Lightning Ridge was found.
In 1904, precious opal was found in South Australia.
Anthropologist Louis Leakey discovered the earliest known opal artifacts in a cave in Kenya. They have been dated to about 4000 B.C. The current theory is that they were mined in what is now Ethiopia, and perhaps sold or traded to people who then returned to what is now Kenya.
Wealthy citizens in ancient Rome loved to acquire opal – it wa srarer than pearls and diamonds. The Roman writer Pliny shares tales of opal coveted by Marc Antony for Cleopatra, in 50 BC.
No one issure where this opal acquired by Roman citizens came from. Pliny believed it came from India, however experts believed that it was mines in what is now Hungary that supplied these gems.
In the Middle Ages, Hungary mined opal which it supplied to Europe and the Middle East. The civilizations of Mexico, Peru and Honduras supplied their own gemstone wants from their opal mines.
Conquistadors returning to Spain brought opal with them in the early 16th century.
However, since the late 1800s, it has been Australia that has dominated the opal market. Austtralia produces 90% of the world’s opal. About 20 other countries supply opal as well – Canada, Ethiopia, Guatemala, Indonesia, New Zealand, Peru, Poland, and Zambia. Gem opal typically comes from the USA, Brazil and Mexico.
View crystal opals on auction at opalauction.com.
Opal is typically categorized based upon its body color – light or dark, as well as the degree of transparency. The body color doesn’t refer to the play of light, but to the actual color of the stone itself, which can be colorless, white, various shades of grey, or black.
Light opal includes all the shades through medium grey
Dark opal includes dark grey to black
In addition, opal can have varying degrees of transparancy, from transparent to translucent to opaque. When an opal is transparent or very translucent, and the clarity of the color is very sharp – the play of color must be both on the surface and within the stone – the opal is called crystal.
Jelly opal is a type of crystal opal that has pla of light within the stone that is hazy, rather than clear.
The samples of Koroit opal below show how beautiful they are, and they are all on auction right now at opalauctions.com
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OLD OPAL MINERS KORIOT OPAL 115 CTS MM 870 opalmania |
50.00 | - | 115 | 5 hours 55 minutes |
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OLD OPAL MINERS KORIOT OPAL HEART SHAPE 170 CTS MM 873 opalmania |
145.00 | - | 170 | 5 hours 55 minutes |
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OLD OPAL MINERS KORIOT OPALRIVER VEIN COLOUR 85 CTS MM 874 opalmania |
150.00 | - | 85 | 5 hours 55 minutes |
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OLD OPAL MINERS KORIOT OPAL HUGE VEINED 328 CTS MM 876 opalmania |
195.00 | - | 328 | 5 hours 55 minutes |
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OLD OPAL MINERS KORIOT OPAL DOUBLE SIDED 130 CTS MM 877 opalmania |
150.00 | - | 130 | 5 hours 55 minutes |
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OLD OPAL MINERS KORIOT OPAL GEM PATTERN 146 CTS MM 879 opalmania |
195.00 | - | 146 | 5 hours 55 minutes |
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OLD OPAL MINERS KORIOT OPAL BUTTERFLY WINGS 170 CTS MM 880 opalmania |
170.00 | - | 170 | 5 hours 55 minutes |
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OLD OPAL MINERS KORIOT OPAL LARGE SQUARE 193 CTS MM 881 opalmania |
115.00 | - | 193 | 5 hours 55 minutes |
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OLD OPAL MINERS KORIOT OPAL TOP COLOURS 98.9 CTS MM 882 opalmania |
125.00 | - | 98.9 | 5 hours 55 minutes |
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OLD OPAL MINERS KORIOT OPAL81 CTS MM 884 opalmania |
125.00 | - | 81.1 | 5 hours 55 minutes |
Again, check out these opals at Koroit opal .
Here are just a few Andamooka Opals on auction at opalauctions.com
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LARGE MATRIX FROM ANDAMOOKA 166 GRAMS [M5B ] sedaopals |
99.00 | - | 23 hours 10 minutes |
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LARGE MATRIX FROM ANDAMOOKA 368 GRAMS [M5A ] sedaopals |
145.00 | - | 23 hours 50 minutes |
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ANDAMOOKA CRYSTAL OPAL 4.20 CTS SFJ 871 (FO-TBO) FOSSIL OPALS |
120.00 | - | 1 day 4 hours |
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ANDAMOOKA STONE -TOP CRYSTAL 7.75CTS [SP1043] PETERS OPAL |
245.00 | - | 1 day 5 hours |
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ANDAMOOKA OPAL PAINTED PARAKEET 135 CTS AB-101 FOSSIL OPALS |
47.00 | - | 1 day 17 hours |
Solid (cabochon) – The opal is left in its natural state. It is only shaped and polished on the cutter’s wheel. If the gem is thick enough, most cutters prefer to cut it en cabochon.
Doublet –A thin veneer of opal, with a dark backing of either black or grey silica material, or a thin slice of common opal cemented to the back of the opal.
Triplet –A slice of quartz may be used to cap the thin opal veneer to protect it from abrasion. This produces a three-tiered gemstone known as a triplet.
Because the doublets and triplets are made with glue, they have a tendency to separate if immersed in water.
Play-of-color – an optical phenomenon, due to the unique formation of the opal. All colors of the rainbow can be seen as the gem is turned this way and that.
The Description of Play of Color:
Harlequin Pattern: The rarest pattern, the colors are arranged in a diamond shape.
Floral Pattern:: The most common pattern – this covers a broad range of design and color.
Pinfire Pattern: Resembles differernt colored pinheads.
Palette Pattern: Resembles an artist’s palette.
Rolling Flash:
Usually consists of one color that travels across part or all of the stone as it is moved. Check out this black opal for an example of rolling flash.
OpalAuctions.com is a site where you can acquire any type of opal under the sun, such as the rare black opal, to jewelry of all kinds, from Australian opals to those from
Brazil, Ethiopia, Honduras, Mexico, Peru, and Tanzania.
It’s also a site where you can join the Forums to talk with other enthusiasts, not just about opals but about selling and buying gemstones, and the gemstones themselves, as well as other collectibles such as coins.
There’s nothing quite like having a place to go on the web where you can share information and just talk with fellow enthusiasts. So check out the forums page at forums.opalauctions.com/.
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