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Short Summary: The first opals were accidentally found on an Australian cattle station called Tarravilla in 1849, and the first opal prospectors started in 1890 at White Cliff.
Around 95 per cent of the opals that are used around the world come from Australian mines.
The first opals were accidentally found on an Australian cattle station called Tarravilla in 1849, and the first opal prospectors started in 1890 at White Cliff The name opal is thought to have been derived from the Latin word opalus, or from the Sanskrit word upala which means 'stone', or 'valuable stone'. In the Roman era the term opalus was used to describe a 'stone made from severa I elements'.
Opals are formed when a mineraloid gel is deposited in fissures of rock, such as limonite, sandstone or basalt, at a low temperature. They have also been known to form or replace fossils, one such famous example being 'Eric' the 85 per cent complete opalised skeleton of a Pliosaur that was found in Coober Pedy, South Australia. Eric can now be seen on display in the National Opal Collection on Pitt Street in Sydney.
Opals generally have a water content of between three and ten per cent, but it can be found as high as 20 per cent. The colours of opals range through the entire spectrum, from white through reds and yellows, greens, blues, pinks and black. The rarest of these colours is red against black, while white and green are the most common.
Opals are a very fragile precious stone, they can scratch and break easily and are quite heat sensitive. As they contain a percentage of water, they can also disintegrate if they dry out. Opal jewellery should be worn as often as possible, as the opal will receive the water it needs from the humidity in the air, or the moisture from the skin of the wearer. They are not a hard stone, rating only 5.5 to 6.0 on the Mohs' scale. Opals used to be oiled in order to protect them, while it is now more popular to seal them with artificial resin or quartz. To care for your opal, wipe it with a soft cloth but do not put it into an ultrasonic cleaner, or let it come into contact with chemicals or dishwater, as this will harm the stone.
Precious and common. Precious opals show a dazzling internal play of colours, while common opals, also known as 'potch', do not. As most of the veins of precious opal are thin, several new methods of preparing the stone have been developed, known as doublets or triplets. An opal doublet is a thin layer of opal backed with another mineral such as basalt or obsidian. This darker background emphasises the play of colour, which results in a more attractive gemstone. An opal triplet has the darker backing, as well as a domed cap of clear quartz, resin or plastic on top, which can be polished to a high finish and acts as a protective layer for the fragile opal. Even though doublets and triplets use precious opal, they are not classed as precious gemstones due to the added materials.
While Australian mines in areas such as Coober Pedy and Andamooka in South Australia, and Lightning Ridge in New South Wales, produce the majority of the world's opals, the remaining five per cent come from Mexico, Brazil, the Czech Republic and in the US states of Idaho and Nevada. Recently opals have also been found in Ethiopia and in Mali, in West Africa, and in early 2008 NASA reported that it had found opal deposits on Mars.
Australia was destined to become the worldwide opal supplier, thanks to a vast Opal jewellery should be worn as often as possible, as the opal will receive the water it needs from the humidity in the air, or the moisture from the skin of the wearer.
Inland sea that once covered parts of what is now desert. Stone sediment was deposited along its shoreline, which combined with water containing silica. The water flushed the sediment into crevices and cavities in the sedimentary rocks, where the silica and sediment combined to create silica stone. Over a long period of time, the silica stone transformed into opal, leaving vein-like deposits throughout the outback.
Mining for opals has generally been a hard job, even with the inventions of machines; as the opals usually occur in veins or fissures in rocks, deep holes are required to excavate the precious stone. The first opals were accidentally found on an Australian cattle station called Tarravilla in 1849, and the first opal prospectors started in 1890 at White Cliff mine. The most famous opal mine is Lightning Ridge, where the highly sought after Black Opal is found, but Andamooka can lay claim to one of the largest opals found - the Andamooka Desert Flame Opal, which weighs in at 6,843 kilograms.
The play of colour in opals is the main reason they are so popular, but up until the 1960s no-one knew how this play of colour came about. A team of Australian scientists analysed opals under an electron microscope and discovered that the small spheres of silica gel that made up the opals caused interference and light refraction. The sizes of sphere can change with different types of opal, resulting in different patterns of light refraction and colour play.
Opals have quite a few different patterns that help distinguish one type from another. Some common patterns include:
Fire Opal - has a translucent red to yellow base colour, with flashes of red, orange and yellow.
Harlequin Opal - has a mosaic pattern of coloured patches and is the most rare and sought after opal.
Pin Opal - has closely spaced flecks of brilliant colour.
Flame Opal - has red streaks or bands throughout the stone.
Flash Opal - has brilliant flashes of colour.
As with many precious and semi-precious stones, imitations are bound to infiltrate the market, opals being no exception. Not long after the mystery behind the colour play in opals was solved. The differences between synthetic and natural opal can be seen under a magnifying glass; synthetic opal has a regular pattern known as 'lizard skin' or 'chicken wire' patterns, while natural opals are susceptible to inclusions and irregular patterns in their colour play. Natural opals will also fluoresce (glow) under UV light, while synthetics won't. Many imitation opals found in vintage jewellery are known as 'Slocum stone', which consists of slivers of foil scattered between laminated glass.
Historically, opals have appeared in myths, been associated with superstition and been held in high regard. The early Greeks believed opals gave them powers of foresight and prophecy, while the Romans saw them as a token of hope and purity. In Australian Aboriginal legends it is said that the creator came to Earth on a rainbow to bring the message of peace, and at the spot his foot touched, the stones came alive with the colours of the rainbow. Around the nineteenth century the superstitions began, with people believing opals to bring bad luck to the wearer, if it were not your birthstone. This superstition still exists to some degree, but many people believe the bad luck is not passed on if the opal is given as a gift. Opal has also been seen as a healing stone, reported to be able to rid depression and help the wearer find true and real love.
They are supposed to enhance positive characteristics of those born under the zodiac sign of Cancer, and black opals are recommended for those born under Scorpio.
The value of an opal is determined by basic factors such as cut, weight and finish, but other factors also come into play when deciding on how valuable an opal is. These other factors include the colours within the opal body colour (basic colour of the gemstone, usually black, grey or brown); transparency; and occurrence. The colours within the opal are a major factor in the valuation of an opal - if there are red flashes in the opal then all other colours will also be present. Black opals are the most popular and expensive as the dark body colour contrasts strongly with the colour play. White or milky opals have more diffuse colours and are usually the least expensive.
The only cut that does the opal any justice is the simple domed cabochon. Faceting an opal doesn't improve the colour play, but can hinder it somewhat instead. Opal cabochons can be mounted using many methods, including bezel and prong settings; but as they are fragile, it is wise to be very gentle. Boulder opals have been known to be used in sculpture and larger scale projects as it is common to cut and polish the host stone as well as the opal. Opal has also been seen as a healing stone, reported to be able to rid depression and help the wearer find true and real love.