Precious Opal

Precious opal is opal that shows play-of-colour: flashes of spectral colours that shift and change as the stone is moved. Opal is a hydrated form of silica (typically 3 to 10 percent water) and is not crystalline but amorphous. In precious opal, tiny spheres of silica are packed together in an orderly grid, and light passing between them is split into rainbow colours, much like a diffraction grating. Common opal contains the same silica spheres but in a disordered arrangement, so it shows no play-of-colour.

Precious opal is grouped by its background (body) colour and setting. White or light opal has a pale body; black opal, the rarest and most valuable, has a dark body that makes the colours especially vivid; crystal opal is transparent to semi-transparent; and boulder opal forms in thin veins within ironstone and is often cut with the brown host rock left on the back. Value depends on the brightness and pattern of the play-of-colour, with patterns such as "harlequin" and "pinfire" given special names.

Australia produces most of the world's precious opal, including black opal from Lightning Ridge, white opal from Coober Pedy and boulder opal from Queensland. Since 2008, Ethiopia (particularly the Welo region) has become a major source of bright white and crystal opal. Some Ethiopian opal is hydrophane, which absorbs water and may temporarily lose its play-of-colour or become transparent when wet.

To make thin slices of opal go further, they are often made into doublets (opal glued to a dark backing) or triplets (with a clear quartz or glass dome on top). Synthetic opal and imitations are also widely sold.

Precious Opal at a glance

Caring for precious opal

Opal is relatively soft (5.5 – 6.5 on the Mohs scale) and contains water, so it is sensitive to knocks, heat and sudden temperature changes, which can cause cracking or "crazing". Clean it gently with lukewarm soapy water and a soft cloth. Never use ultrasonic or steam cleaners, and do not soak doublets or triplets, as water can loosen the glue. Avoid chemicals and strong sunlight. Store opal separately in a soft pouch, away from harder stones.

In folklore

The beliefs below are traditional folklore, included for interest. They are not scientifically proven, and nothing here is medical advice.

The Romans prized opal above almost all other gems, believing it contained the colours and powers of all other stones, and Pliny the Elder described it in detail. In the Middle Ages it was considered very lucky and was said to make its wearer invisible. In the 19th century, the novel "Anne of Geierstein" by Sir Walter Scott linked opal with bad luck, and sales fell sharply; Queen Victoria later helped restore its popularity. Aboriginal legend in Australia tells that opal was created where the Creator's foot touched the earth in a rainbow. Opal is the birthstone for October and the gift for a 14th wedding anniversary, and is associated with the zodiac signs Libra and Scorpio.

Precious opal is traditionally regarded as a stone of inspiration, creativity and emotional expression. Crystal healing lore holds that it amplifies the wearer's feelings, encourages spontaneity and imagination, and brings hope and optimism. It is also associated with love and passion. It is linked to the crown chakra.

Related stones

Fire opal, common opal, boulder opal, black opal, crystal opal, opal doublets and triplets, and synthetic (created) opal. Other stones with play-of-colour or sheen include labradorite, moonstone, ammolite and fire agate. Imitations include opalite glass, plastic and resin.

For the technically minded

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