Opal: meaning, properties and lore

The mineral

Opal is classified as hydrated silica, and silica is a compound of silicon and oxygen. Gem-grade opals usually hold 6% to 10% water, and opal can contain up to 20% water trapped in its silica structure. Its specific gravity is 2.15 (+0.08, -0.90), and its refractive index runs from 1.37 to 1.47. Opal has relatively low density compared with many other gemstones.^1327894

Opal's play-of-color comes from sub-microscopic silica spheres stacked in a grid-like pattern that diffract light into spectral colors. Spheres about 0.1 micron across produce violet play-of-color, while spheres about 0.2 microns produce red. Play-of-color is the defining characteristic of gem opals, and precious opal displays it while common opal does not.³¹²⁵

Opal's bodycolor differs by type. White or light opal is translucent to semitranslucent with play-of-color against a light background. Background colour is caused by tiny impurities suspended within the silica spheres.³⁴

Opal has a Mohs hardness of 5 to 6.5, and it is not as hard as many gems, so it is vulnerable to scratches and chips. Opal can craze when it loses moisture, forming a fine network of cracks, and moisture loss is caused by heat, excessive dryness or bright light.¹²¹⁰⁹⁴

Opal forms when silica gel fills crevices in rock and water evaporates, leaving silica deposited as tiny spheres. Seasonal rains carry dissolved silica deep into ancient underground rock, and water evaporating in dry periods leaves those deposits behind. Opal has a species-level status and is described as a class by itself with its own descriptive vocabulary.¹³²¹¹⁷

Approximately 90% of the world's opals are from Australia, and Australia's mines became the world's primary source after commercial production began in the 1890s. Opal occurs at Lightning Ridge, Mintabie and Coober Pedy in South Australia, and South Australia is one of the few places on Earth where very large opals are found. Boulder opal occurs in thin veins through hard ironstone boulders, and was discovered about 1875 in western Queensland. Black opal was discovered in 1903 at Lightning Ridge near Walgett, New South Wales, by Charlie Yettleton, an old prospector.⁴¹³¹²

Opal is also found in Mexico, the United States, Honduras and Peru, and Fine opal comes from many localities. Ethiopian opal from the Wollo Province contains fossilized plant material as inclusions, and Australian opal can contain pyrite crystals and black plumes of manganese oxide. Chilean blue opal is reportedly from the Atacama region, the only known occurrence to date in Chile, where chrysocolla is common in porphyry copper deposits. Peruvian blue opal, known as Andean opal, is generally translucent and lower in saturation than Chilean blue opal.⁵¹⁰⁶

History and lore

The Romans named the gem opalus, a word synonymous with 'precious stone', and in ancient Rome opal symbolized love and hope. Roman scholar Pliny, writing in 75 AD, described opals as carrying a play of colour that equals the deepest and richest colours of painters. Pliny marveled that opal encompassed the red of ruby, the green of emerald, the yellow of topaz, the blue of sapphire and the purple of amethyst. The Romans thought opal was the most precious and powerful of all gems because it has the colors of other gems. Pliny also said it was found in India, Egypt, Cyprus, Thasos and other places.¹³¹¹¹

Arabic legends say opal falls from the heavens in flashes of lightning, and the Bedouins believed that opals contained lightning and fell from the sky during thunderstorms. The ancient Greeks believed opals gave their owners the gift of prophecy and guarded them from disease. Opal was once thought to have the power to preserve the life and color of blond hair. Throughout most of history it has been regarded as the luckiest and most magical of all gems because it can show all colors.¹³¹

Gesenius translated the Hebrew stone Lesham as opal, and Dr. M. H. Breslau accepted that reading. Dr. E. G. Hirsch stated that the seventh stone of the Breastplate must be brilliant and of intense lustre. Mr. King mentioned an antique Roman opal intaglio in the Praun collection engraved with the heads of Jupiter, Apollo and Diana. The ancients called opal 'Cupid'.¹¹

Sir Walter Scott's novel Anne of Geierstein, published in 1829, gave opal a reputation of being unlucky, and the superstition that opal is unlucky for those born in other months comes from that novel rather than from any ancient belief. Opal has a rich body of folklore, and opal gems have been considered both the luckiest and unluckiest stones to wear.¹¹³²

Shakespeare, in Twelfth Night, called opal the Queen of gems, a miracle of gems. Orpheus declared that the opal fills the heart of the gods with joy, and the ancient Greek writer Onomacritus said that the delicate colours and tenderness of the opal remind him of a loving and beautiful child. Mark Antony coveted the opal ring of Nonius to give to Cleopatra, and banished Nonius for refusing to part with it.¹²

Opal was known centuries before Christ and was prized above all other gems, becoming the symbol of hope and purity. Opal loses colour on exposure to air, and its colour can be restored by leaving it some time in oil.¹²¹³⁹

Synthetic opal was first made in the early 1970s when John Slocum of Rochester, Michigan introduced an imitation of metal foil embedded in glass that produces thin-film interference colours. In 1972 Pierre Gilson began manufacturing a true synthetic opal that did not require polymer impregnation.⁵

Birthstone and other links

Opal is an October birthstone, a link set by the birthstone list that the claims attribute to the Gemological Institute of America. Opal is the stone given to celebrate the 14th wedding anniversary, a link that crystal practitioners make.¹³¹³²⁴

Crystal practitioners say that opal is unlucky for anyone born in another month to wear it, although that superstition traces to Anne of Geierstein rather than to ancient belief.¹³

What crystal practitioners say

Crystal practitioners associate opal with the mind and with clear thinking, and they describe it as a stone whose appeal lies in artistry. Noble Opal is said by the book's author to remind one of one's original goals and the colourful, creative ideas of one's life dream. Opal is said to bring joie-de-vivre and hope in hopeless circumstances, and to motivate one to take care of oneself.¹⁴¹²

Practitioners say that opal can help with hardship and worries, and the Healing Crystals First Aid Book says it does not cure the root cause of the problem. Noble Opal is said to make it easier to come to terms with grief and let go of fixation on its cause.¹⁴

Opal lovers prize bright play-of-color over faint play-of-color, and red is traditionally considered the best prominent color.¹⁰⁴

Crystal healers claim that Noble Opal ensures tissues and lymph are cleansed, improving nutrient supply to cells and waste removal, according to The Healing Crystals First Aid Book. The same book says Chalcedony and Noble Opal provide rapid relief from all kinds of coughs and encourage expectoration.¹⁴

Practitioners advise keeping opal out of bright light, heat and excessive dryness, since these conditions can harm the stone.¹⁰⁴

What testing has found

Edzard Ernst, who analysed 150 complementary and alternative treatments, found no rigorous trials testing crystal healing's therapeutic value. He stated that no scientific proof exists of any effect beyond placebo, and that crystal healing can generally be regarded as harmless and without toxicity.¹⁵

In 2001 Chris French, a British psychologist, ran a double-blind study with 80 participants who meditated with either a real quartz crystal or a fake glass one. Participants could not distinguish real quartz from glass, and both groups reported similar impressions, which the researchers read as a placebo effect. Euronews reported that the French team concluded suggestion, rather than the crystals, helped people. Larger studies have not replicated these results.¹⁵¹⁶¹⁷

Some researchers suggest crystals probably do not act directly on physical or psychological complaints, though they may offer indirect benefits linked to the placebo effect. Ted Kaptchuk, a Harvard Medical School professor, argues that placebo effects should remain part of any analysis of unconventional medicine. Rigorous research into crystal therapy is still lacking, and scientists remain skeptical.¹⁶¹⁵