What is Opal?
Australia's Hidden Treasure
Mysterious opals contain the wonders of the skies ‐ sparking rainbows, fireworks, and lightning ‐ shifting and moving in their depths.
Opal has been treasured throughout history around the world. Archaeologist Louis Leakey found six thousand year old opal artefacts in a cave in Kenya!
Roman historian Pliny described the beauty of opal as the combination of the beauty of all other gems: "There is in them a softer fire than the ruby, there is the brilliant purple of the amethyst, and the sea green of the emerald ‐ all shining together in incredible union. Some by their splendour rival the colours of the painters, others the flame of burning sulphur or of fire quickened by oil." Opal was much loved and valued highly by the Romans, who called it opalus. At the same time, opal was also sought in what would become the Americas. The Aztecs mined opal in South and Central America.
Opal was also treasured in the Middle Ages and was called ophthalmios, or eye stone, due to a widespread belief that it was beneficial to eyesight. Blonde women wore opal necklaces to protect their hair from losing its colour. Some thought the opal's effect on sight could render the wearer invisible. They were recommended for thieves!
Opals are set in the crown jewels of France. Napoleon gave Josephine a beautiful opal with brilliant red flashes called "The burning of Troy," making her his Helen. Shakespeare found in the opal a symbol of shifting inconstancy, likening play of colour to play of mind in one of the most apt uses of gemstone symbolism in literature. In Twelfth Night, he writes: "Now the melancholy God protect thee, and the tailor make thy garments of changeable taffeta, for thy mind is opal."
In the nineteenth century, opal was considered unlucky due to the plot of a popular Sir Walter Scott novel of The time. The heroine of the novel has her life force caught in the beautiful opal she wears in her hair and she dies when the fire in the opal is extinguished. However, Queen Victoria loved opals and often gave them as wedding presents. She and her daughters created a fashion for wearing opal. Queen Victoria was one of the first to appreciate opals from an exciting new source: Australia.
The story of opal in Australia begins more than 100 million years ago, when the deserts of central Australia was a great Inland Sea, with silica-laden sediment deposited around its shoreline. After the sea receded and disappeared to become the great Artesian basin, weathering 30 million years ago released a lot of the silica into a solution which filled cracks in the rocks, layers in clay, and even some fossils. Some of this silica became precious opal.
Opal is one of the few gemstones that are sedimentary in origin. Opal still contains 6 to 10 percent water, a remnant of that ancient sea. Gold panners in Australia found the first few pieces of precious opal in 1863. Mines at White Cliffs began producing in 1890.
A large percentage of the world�s stable commercial opal comes from Australia, and there are three distinctive regions where opal comes from. These are Lightning Ridge (the home of black opal) the South Australian fields Coober Pedy, Mintabie, Lambina and Andamooka (the main sources of light base opal) and the Queensland fields, where boulder opal originates.
The major opal producing fields for black opal is Lightning Ridge in New South Wales, Australia, and to a much lesser degree Mintabie in South Australia. The most sought after black opal is red or multicolour on black, which is very difficult to find. Such stones are always cut on the fields and sell immediately.
Boulder opal is opal that has formed in a brown ironstone nodule, and is distinctive because it typically presents as a thin layer of opal over a dark brown base when cut. The opal can be quite superb.
Opal from Lightning Ridge is often considered to be the best and brightest in the world.
What is Opal?
Opal is a non-crystalline form of the mineral silica, which, despite its amorphous structure, displays an Amazing degree of internal organisation. Opal is related to its more commonly found but highly crystalline cousins quartz and agate, and is formed from amorphous "balls" or lumps" of silica rather that from ordered, naturally faceted crystals.
The chemical composition of opal is SiO2H2O, silicon dioxide combined with water (an opal stone may contain up to 30% water.) The silicate minerals in the stone add to its weight, giving it a specific gravity ranging from 1.98 to 2.5 times that of pure water. Opal's scratch hardness is measured at 6.0 to 6.5 on the Mohs' scale, similar in hardness to quartz, a little more than halfway between the hardness of talc and diamond.
Most opal is more than 60 million years old and generally dates back to the Cretaceous period when dinosaurs roamed the earth
It is found near the earth's surface in areas where ancient geothermal hot springs once flowed. The minerals bubbled up from beneath the surface of the earth and slowly, over the centuries, lined the walls of cracks, vents and underground cavities in the bedrock. Most opal is found where geothermal hot springs dried up during seasonal periods of rainfall and extended dry periods.
More than 90% of the world's quality gem opals come from Southern Australia, although it can be found in other parts of the world such as Brazil, Mexico, Czechoslovakia and Nevada. All black opal comes exclusively from Australia.
The story of opal in Australia begins more than 70 million years ago when the deserts of central Australia were an Inland Sea, with silica-laden sediment deposited around its shoreline. After the sea receded and disappeared to become the great Artesian basin, weathering 30 million years ago released a lot of the silica into a solution which filled cracks in the rocks, layers in clay, and even some fossils. Some of the silica became precious opal. Opal is one of the few gemstones that are sedimentary in origin. The water in opal is a remnant of that ancient sea.
The most striking quality of opal is its ability to refract and reflect specific wavelengths of light. In fact, the term "opalescence" was coined to describe this phenomenon. The size and spacing of the amorphous spheres of silica within the stone refracts specific wavelengths of light; each sphere refracting a single, pure spectral colour much like the individual microscopic droplets of water in a rainbow. The interplay of these pure wavelengths of light gives opal its unique visual appeal, and makes it one of the most sought-after gemstones in the world.
Birthstone Months with Opal
April: Mystical Birthstone
October: Modern and Ayurvedic Birthstone
Aquarius (Jan 20-Feb 18): Birthstone
Libra (Sep 23-Oct 22): Birthstone/Lucky Charms
Anniversary Gemstone for Opal
Opal is the Anniversary gemstone for the 14th and 18th years of marriage.
Opal Mystical Properties
Opal is used to see possibilities.
Science has told us this about opal
CHEMISTRY: SiO2. nH2O. Water usually 6 to 10% in precious opal, can be as high as 21%
REFRACTIVE INDEX: 1.44 - 1.47
HARDNESS: 5.5 - 6.5
SPECIFIC GRAVITY: 1.99 - 2.25
Opals around the world
Opal is derived from the Latin word Upala that relates to precious stones and was considered the cupid paederos or child as beautiful as love. Roman scholars described opal as having the green colour of emerald the brilliance of amethyst and that opal represented hope and purity which was later adopted by modern Asian countries who consider the opal as an anchor of hope. The opal that the Romans referred to were from the present day country hungry and was crystal formed volcanic gemstones in the Carpathian mountains with flashes colour that was not seen any where else in the ancient world and really impressed the Romans.
Ancient Greeks believed opal had the power to have sixth sense in foresight and also prosperity. Cleopatra is said to have worn and opal to attract Mark Anthony.
Native Australian called aborigines’ have long history going back thousands of years and they considered opal to have spiritual properties and have many myths and legends about Opal.
They believe opal holds signs of their past ancestors and is sign of their presence and also a spirit named Muda who changes from man to pelican so pelican birds are considered spiritual also.
Asian countries had experienced opals from Indonesia and appreciate the colour spectrum of opals compared to gemstones such as ruby and sapphire which are mined in asia.
The opal has been considered as a gemstone of hope and security .
In Japan they buy opals as show of wealth and standing in the community as prefer perfect formed gem quality even if opal is small.
Opal is one of the world’s most spectacular gemstone and fortunately for those born in October it is their Birthstone.
This is under the Modern Birthstone chart.
For the traditional Birthstone chart Tourmaline is considered the birthstone.
For the Mystical birthstone chart Jasper is considered the birthstone.
And for Ayurvedic Birthstone chart Opal is also considered the Birthstone.
The Ayurvedic Birthstone list is from Ayurvedic Indian Medicine - a type of medicine used for over a thousand years
Now days we use the Modern birthstone chart so Opal is now strongly associated with October birthdays.
Opal is also considered the mystical birthstone for April.
Mystical Birthstone chart is the Tibetan thousand year old version and opal in those days are more closely associated with quartz gemstones that present day opals.
Opal is considered as the gem Of the Gods and has mystical significance and is said to help in physician vision and to open our spiritual centres.
Opal is also believed to heighten weak emotions and to strengthen memory.
The word evolved from the Greek word "opallus" meaning to see a change in colour. Later the Latin word "opalus" came to mean precious stone.
Opals stand in a class by itself. More than any other gem, each opal is distinctly an individual. No other stone has as rich and varied folklore. Opals are so unique they have their own descriptive vocabulary. They are the most delicate gems that are commonly worn. Opal's fire was long thought to be the result of iridescence. However, with the advent of scanning electron microscopes, we now know that it is a result of diffraction.
Opal is an amorphous form of silica, (SiO2.nH2O) chemically similar to quartz, (SiO2) but containing 3% to 21% water within the mineral structure. Gem grade opals are usually 6% to 10% water content.
Opal is a sedimentary stone. Under proper conditions, water percolates through the earth, becoming rich in dissolved silicates. When it enters a cavity, the silicates are deposited as tiny spheres. If they are uniform in size and shape, they will diffract light. If they are random in shape and arrangement, we have common opal.
Volcanic ash gives black opal its colour, but inclusions have nothing to do with the play of colour. That is due entirely to the tiny spheres. They must be smaller than 1500 angstroms for blue and violet colours, but no larger than 3500 angstroms to produce oranges and reds. To put that in perspective, 20,000 spheres are about the size of the period at the end of this sentence.
Opal grows by filling in cavities, regardless of their shape. Hence, we have many pseudo morphs, materials with shapes that are unrelated to the chemical content. The most common are Opalised wood and seashells. source: www.gemsociety.org