Thursday, October 13, 2011

Opal is October's birthstone and the Gemstone of the Week

Opal is the featured gemstone this week, because it is also the birthstone for October. Often called nature's fireworks, this gemstone is composed of hydrated silica. Since the structure is not truly crystalline, it is considered a mineraloid, rather than a mineral. Opal has the same chemical composition as quartz, but has a water content between 3% and 21%, although the average water content is between 6% and 10%. Fine examples of opal can be more valuable than diamonds. It is a somewhat soft stone. On the Moh scale, it has a hardness of 5.5-6.5.

The internal structure of opal makes it defract light and, depending on the conditions in which it was formed, the stone can take on many colors. These colors can range from clear, white, gray, yellow, orange, green, blue, magenta, rose, pink, slate, olive brown and black. Red hues against black are the most rare, with white and green being the most common. The iridescent color flashes, are called opalescence, and change depending on the angle from which the stone is viewed.

Most opal is over 60 million years old, which dates it back to the time when dinosaurs roamed the Earth. Opal has been considered a gemstone since Roman times when it was considered to be second in value only to emeralds. The name, “opal” probably comes from “upala”, the Sanskrit word for precious stone.

Opals are usually sold in one of three ways. The solid gemstone by itself, although it is usually enhanced by some type of wax treatment to protect it from drying out. Opal doublets are thin slices of opal glues to a base material such as ironstone, basalt or obsidian. The darker color backing emphasizes the play of colors in the gemstone. Opal triplets are doublets topped with a domed cap of clear quartz, resin or plastic. This protects the relatively soft stone from scratches, while magnifying the play of colors in the stone.

Opals are most commonly from Australia, but are also found in the Czech Republic, Turkey, Indonesia, Brazil, and in the United States, in Nevada. In 2008, NASA also announced that they had found opal deposits on Mars.

Opal is believed to aid in the healing of eye diseases, enhance creativity, and to foster love and warmth. The ancient Romans considered the stone to be one of good fortune, while the Russians considered it to be bad luck. Queen Victoria loved opals and she and her daughters created a fashion trend for opal jewelry.
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Rough opal from a Nevada mine

The Queen's Opal weighs in at 203 carats or 41 grams.

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