What Is an Opal?
The opal: a delightful quirk of nature, a wonder to behold. Mystery and myth surround this rich and lustrous stone. There is nothing else on earth quite like SiO2 - nH2O--that is, hydrated silicon dioxide, a mineraloid that fashions into one of the world's most popular and glamorous gems.
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History
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Opals have charmed people for millenia, in civilizations throughout the world. Early Greek, Roman and Arabic cultures were among the first to prize the opal for its fiery beauty and the first to proclaim its mystical properties. The oldest known opal objects, found in East African caves, dated back to 4000 BC.
Myths and Mysteries
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Throughout history, cultures have claimed a mysterious, spiritual connection between the opal and its wearer. Some societies believed that opals intensified emotions, giving humans clearer insight and wisdom. Others gave religious significance to the jewels. Various civilizations attributed many other unusual powers to opals: promoting good eyesight, lowering inhibitions, preserving hair color, and effecting invisibility. Europeans became afraid of opals at the beginning of the 19th century, thinking that they brought bad luck. Myths of the opal continue even today. It is commonly felt that opals, being the birthstone for October, should only be worn by those born in that month. Whether these notions are fact or fallacy, the opal's otherworldliness has now been substantiated. According to the British Broadcasting Corporation (BCC), an American space probe discovered opals on Mars in 2008.
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Chemical Composition of the Opal
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Some scientists have classified the opal as a member of the quartz family. However, quartz is a mineral, and opals are NOT true minerals. They do not have a regular arrangement of atoms in their structure. Rather, opals are "mineraloids." Each opal contains anywhere from 5 to 10 percent water as well as random chains of silicon and oxygen that are packed into tiny spheres. These spheres are clustered in precious gemstone opals, and their pattern of arrangement helps to determine the refraction of light which results in the rainbow of colors referred to as "play of color" or "opalescence."
Kinds of Opals
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There are countless varieties of opals. In fact, every opal is unique. Geologists have categorized opals by use, body color, fire and place of origin. First, opals are either "precious" or "common." Precious opals are gem-quality stones. These are the ones that dazzle the eyes of the beholder with brilliant flashes of spectral color and light, referred to as "play of color." Common opals lack the opalescent quality of fiery iridescence. Rather, they are as their name implies, plain. Another name for common opal is "potch." Potch is often used as a base stone to which a thinner layer of precious stone is applied.
Next, opals are classified according to their color and body. There are four basic types: white or milky opal, black or dark opal, fire opal, and boulder opal. White opals are the most common and least expensive gemstones. Black opals are the least prevalent and most costly.
The pattern of fire emanating from within the stone is another way of classifying opals. The harlequin opal displays diamonds of brilliant color variations and light patterns. Contra luz opals are clear and show plays of color only when a light is placed behind the stone. Pinfire or pinlight opals show colorful specks of light. The play of color in cat's eye opals consists of narrow strips of interplaying fire.
Opals are also named according to the locations in which they are found. A little less than 95 percent of the world's opals are from Australia. The United States produces opals mostly in Idaho, Oregon and Nevada. Opals are also found in Mexico, Peru and a few other countries.
Uses of the Opal
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Opals are relatively fragile, about the same as glass. Some opals are harder than others. For instance, white or milky opals are more likely to crack or craze than transparent opals. Opals are given a rating of 5.5 to 6.0 on the Moh's scale, which ranks the hardness of minerals from 1, the softest (talc), to 10, the hardest (diamonds).
Because of their physical vulnerability, opals are not used for industrial purposes. Their purpose is purely to decorate and enchant the lives of those who wear them and observe them.
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Resources
- Photo Credit Photo supplied by Opals Down Under Queensland, Australia www.opalsdownunder.com.au
