Searching for real opals? You should be familiar with the characteristic optical features that a natural, untreated opal exhibits. To check the authenticity of the opal, get it under a Turbidity meter. All opals exhibit an optical phenomenon derived from their own primary name- opalescence. It is defined as the milky and turbid appearance in opal.
Opals: The Magic of Milky White
Often referred to as the stone from the Cosmos, opal is a Sanskrit word- Uppal meaning “precious milky stone”. It is a gemstone largely constituted of hydrated silicon di oxide. It is an amorphous stone and is extracted largely from the Southern Hemisphere. In fact, it is actually the National Gemstone of Australia.
The various forms of opal are:
1. Precious Opal
2. Fire Opal
3. Potch Opal
4. Girasol Opal
5. Blue Opal Gemstone, also called Peruvian opal
Opals actually exhibit both Play of Colour as well as Opalescence.
How opalescence occurs in the gemstone?
Opalescence is confined largely to the blue spectrum during reflection of short wavelength light rays. It is because of this phenomenon that a gemstone appears turbid with a shiny blue surface. Another reason, it appears blue is due to the significantly high traces of water, which could be as much as 21% of the silica crystal volume.
The spaces where water is present hinder the passage of light, making the gemstone look milky. Through these spaces, no diffraction occurs. The internal scattering around the water traces render the opal its characteristic opalescence.
Opals that made History
Opalescence can occur along with white, colourless, yellow, red, grey, black and fiery shades of red and blue as well. Diffraction causes flashes of Play of Colour. Intensity of opalescence decides the brilliance and clarity of the gemstone, and hence commands the price. The red opal beads as well as blue opal beads are extensively used in jewellery.
Opals in flat cabochon glorify the opalescence in the most beautiful way. The most popular opal gemstones in the history of mankind are:
Sun God Opal:
A 16th century gemstone, carved from mines in Mexico. It is a 35 carat Aztec-era stone with a singular quality. It is a dazzling item showcasing opalescence and play of colours brilliantly.
Dark Jubilee Opal:
A thrilling example of Australian opal deposits, this 314.8 carat gemstone was mined from Coober Pedy.
The Olympic Australis
Named after the Olympic Games in Melbourne, this is one of the purest mega-carat gemstone ever mined. Valued at $2,500,000 (Australian Dollars), it is a massive 17,000 carat opal exhibited all over the world.
The Butterfly Stone
Also named as the Red Admiral, it is a unique gemstone exhibiting opalescence at only certain angles. It resembles the red English butterflies and hence the name.
Empress of Australia
Rightly named, this gemstone was mined in 1915. It is referred to as ‘Kaleidoscope Queen’ and ‘Tartan Queen’. It weighed 500 carats in its initial days of glory.
Other prominent opals owned by museums and individual collectors are Pride of Australia, The Flame Queen, The Black Prince and Halley’s Comet.