Opal is Australia’s national gemstone, and the most magnificent and colourful of precious gems. Like all fine things, precious opal is exceedingly rare.
Opal can boast any colour of the visible spectrum, from deep clear blues and greens to golden orange; from delicate pink and violet to rich turquoise, shocking red or fuschia. An opal may contain any or all of these colours in wondrous patterns with evocative names: harlequin, pin fire, Chinese writing, flower garden, mackerel sky, flagstone, rolling flash, and others.
The majority of the world’s precious opal is mined in Australia’s harsh outback, in the states of New South Wales, Queensland and South Australia. Many millions of years ago, a unique combination of geological conditions around an ancient inland sea permitted the formation of the world’s greatest opal deposits.
Australia is regarded as the world’s leading source of opal and of the world’s finest opal. In 1994, opal was declared Australia’s National Gemstone.
Unlike the colors of most other gemstones, color in opal isn’t caused by mineral inclusions. The main ingredient in opal is silica – the most abundant mineral in the Earth’s crust and most commonly found as sand or quartz. Silica is also the main ingredient in materials such as glass, concrete and even toothpaste.
In precious opal – the name given to opal with spectral colours, or ‘play of color’ – the tiny spheres of silica dioxide are uniform in size and stacked in regular rows and layers. This configuration creates lattices that diffract white light into different colours of the spectrum. The tiniest spheres produce violet-coloured opal; the largest, red, with sphere size increasing from the violet to the red end of the spectrum.If the spheres are jumbled, there is no play of colour and the opal looks grey, black, white or amber-colored Called ‘common opal’ or ‘potch’, this account for over 90% of opal found.
No other gemstone can display all the colours of the spectrum in such an infinite variety of shades, patterns and brilliance.