Opal is the birthstone of people born in October.
The name is believed to have originated in India, where in Sanskrit it was called upala meaning ‘precious stone’.
Most Opals are cherished and valued for their shifting rainbow colours – a phenomenon known as ‘play of colour’.
Introduction and Colour
Opal is one of the most colourful gemstones found in the world. It is an eclectic mix of colours and unsurpassed in its splendid display. Some of them are more valuable than diamonds too. The stone is such that the iridescent colour flashes change with the angle from which the stone is viewed at. This is known as opalescence. The play of colour may comprise large, individual flashes of colour (known as schillers), or tiny, dense flashes. The value of an Opal is dependent on the intensity and distribution of the colour flashes. Opals come in a range of colours – white, colourless, blue, red, green, yellow, orange, brown, pink, purple, grey, black, banded, multi-coloured.
Formation and chemical composition
Opal is formed when seasonal rains drenched dry ground in regions such as Australia’s semi deserts. Carrying dissolved silica (a compound of oxygen and silicon), the rains soaked deep into the underground rock. During the dry periods, much of the water evaporates, leaving solid deposits of the silica between the underground and sedimentary rocks in layers. The silica deposits then form Opal.
Opal being amorphous, is a mineraloid, not a mineral. Opal lacks a crystal structure, which is found in all minerals. The chemical composition of Opal is SiO2H2O i.e. silicon dioxide combined with water. An Opal gemstone may contain up to 30 percent water.
History of Opal
In 75 AD, the Roman scholar Pliny compared opals to volcanoes and dancing paintings while observing that their dancing play of rainbow colours could simulate shades of any gemstone. He marvelled at how this kaleidoscopic gemstone captured the red of the ruby, the blue of sapphire, the green of emerald, the yellow of topaz and the purple of amethyst.
There are many legends across centuries that surround Opals. It was thought to bring the wearer luck during the Middle Ages. However, this changed when Sir Walter Scott wrote a best-selling novel in 1829 called Anne of Geuerstein, where a character Lady Hermione, falsely accused of being a demoness, dies after a drop of holy water falls accidentally on her opal and destroys its colour. The public is misunderstood as opals being bearers of bad luck. For nearly 50 years, the opal market crashed by 50 percent.
But this changed in 1877, when opal deposits were found in Australia and an amazing black opal was found in South Wales. The country began producing 95 percent of the world’s Opal supply.
Opal species and varieties
There are five main types of Opals:
- Black Opal – They range from translucent to opaque and have a play of colour against a dark or black background.
- White or light Opal – They have a play of colour against a white or light grey background called body colour. They range from translucent to semi-translucent.
- Fire Opal – They range from transparent to translucent and come in a variety of body colours – brown, yellow, orange or red. They don’t often show play of colour and are also known as “Mexican Opal”.
- Crystal or water Opal – It has a clear background and ranges from transparent to semi-transparent. This particular type of Opal shows an exceptional play of colour.
- Boulder Opal – As the name suggests, they are transparent to opaque with play of colour against a light to dark background. In this Opal, parts of the surrounding rocks where it is found become a part of the finished gem.
Beliefs
Many cultures believe Opals have supernatural origins and powers. Arabic legends say that Opals fall from the heavens during flashes of thunder and lightning. For the ancient Greeks, Opals gave their owners the gift of prophecy and protection from disease. For a long time, Europeans have held Opals to be a symbol of hope, purity and truth.
In ancient Rome Opals symbolize love and hope. The Romans called it – opalus – synonymous with ‘precious stone’.
Importance of Opal in astrology
Astrologers associate Opal gemstones with the planet Venus. Venus is said to deal with luxuries, comfort, love, wealth, beauty etc in one’s life. It is said wearing Opal boosts positivity in these aspects of life. The stone is highly effective in Mahadasha/Antardasha of Venus.
According to Vedic astrology, Opal can be worn by those born under Libra and Taurus sun signs. It is often used as a substitute for diamonds in astrology.
Opal is also said to spark passion in life and increase creativity and bring good fortune to the bearer.
Healing benefits
This gemstone is believed to create a balance between the right and left sides of the brain. It provides neuro-stability to the one wearing it and promotes speedy recovery from shaky hands or those who suffer from Parkinson’s disease. It is also said to cure other health problems related to throat, spleen, reproductive organs, pancreas etc.
Physical and optical properties of Opal
It is a hydrated silica with a refractive index of 1.37-1.47. It ranges from 5 to 6.5 on the Mohs scale of hardness. Opal has a specific gravity of 2.15. Its lustre is usually vitreous but can also be pearly, waxy or resinous. It is usually transparent to opaque in appearance and a visible lack of cleavage.
Demand and scope
Opal is quite popular in the Indian and international market. In India, the price starts from Rs 250 per carat and can go up to Rs 5000 per carat depending on various factors such as shape, clarity, origin etc.
Famous Opals
The world’s largest and most valuable Opal was found in 1956 during the Olympic Games in Melbourne. It is called the Olympic Australis and came from Coober Pedy in Australia. It was valued at $2.5 million in 2005 and weighs 17,000 carats (7.6 pounds).
Identification of Opal
For practical identification of Opals, click on the link below.
Gemology Graduate
Treatments
Some of the common treatments of Opals is the use of resins or wax to seal the cut stone. Doing this improves shine and prevents dehydration. Sometimes white opals or crystal opals are smoked to make it look more like black Opal. An opal that has been treated to become dark is more valuable than a white opal.
Pricing
Multiple factors determine the value of an Opal. The type of opal, body tone, brilliance, pattern, colour bar thickness, the play of colour, and faults all play important roles in determining the value.
Other important factors include the quality of the cut & polish, and the size of the stone. When being valued, opal is carefully examined and given a price ‘per carat’. The overall carat size of the stone will then determine the price of the opal.
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