Opal
The word Opal comes from the Latin word "opalus," which means precious stone. Opal is a form of noncrystalline quartz which is created from circulating, silica-bearing waters. When the silica solidifies it creates the gemstone Opal which contains approximately 6 to 10 percent water. Opal is commonly found in volcanic rock, especially near geysers and hot springs, but can occur in almost any geological environment.
Pure Opal is primarily colorless, but impurities usually impart various colors to it ranging from yellows and reds. due to iron oxides, to black from manganese oxides and carbon. Black Opal, with a very dark gray or blue-to-black color, is rare and highly prized. White Opal, with light colors, and Fire Opal, with yellow, orange or red colors, are much more common.
Precious Opals are translucent to transparent and have a pearly opalescence revealing many flashing colors, which change as a stone is viewed from different angles. This milkiness in many white and gray opals is due to an abundance of tiny gas-filled cavities.
When warmed by the hand, water contained within an Opal stone can change the colors, making them particularly brilliant. Opals can be dehydrated when exposed to heat or chemicals. Many chemicals can damage an Opal due to its porous structure.
Various forms of common Opal are mined for industrial used in abrasives, ceramics and insulation. Scientists have been able to reproduce synthetic Opal in a laboratory, and other "simulants" exist on the market. Simulants are man-made stones which are similar to Opal but made from a different material.
Fire Opal is minded in Mexico and Honduras, and several varieties of Precious Opal are found in India, New Zealand and the deserts of the western US. In ancient times Opal was considered to be a noble gem, and the Romans ranked it second only to the Emerald. In the Middle Ages it was said to bring good luck. Most Precious Opal mined in ancient times came from what is now Slovakia.
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Crystal System
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None
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Fracture
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Conchoidal
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VARIETIES
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Color: Transparent to milky white appearing in white, grey , red, brown, blue, green, andblack. Luster: Most Opal has a vitreous (glass-like) or pearly finish, but some are resinous or dull. Transparency: To translucent, sometimes highly fluorescent. |
Common Opal: Translucent, pale in various colors, but lacks the reflective colors of precious Opal. Precious Opal: Milky white or black in color with reflections of brilliant colors such as, blues, reds, & yellows. Fire Opal: Red and yellow colors are dormant which create flame-like reflections. Hyalite: Has no color. Hydrophane: Becomes transparent when placed in water. Wood Opal: Is wood that has been partially replaced by Opal silica. |
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