Opal

From ArticleWorld


Opals are found in a variety of colors ranging from colorless to white, milky blue, gray, red, yellow, green, brown and black. Although the more common opals are crooked and shapeless, a precious opal has a proper form and structure. Opal has a hexagonal or cubical structure closely packed with silica spheres measuring between 150nm to 300nm in diameter. These spheres of silica cause the diffraction that results in the display of colors in the stone. The term 'opalescence' describes the opal’s most beautiful and unique feature, the play of colors. However, the common opal, or 'potch', does not display this unique feature.

The veins of opal are extremely thin, thus resulting in play of colors. Sometimes if backed by a black mineral such as ironstone, basalt or obsidian, a thin layer of material, called opal doublet, displays darker and more prominent colors. They may also be backed by a darker material and have a top cover of clear quartz for better polish and protection.

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Common opal

There are many other more common opals that display colors, but they are not the same as the gemstone. Some of them are milk opals which are milky, bluish, or greenish. Another, resin opals, are honey-yellow with a resinous look. Others include: wood opals; menilite, which is brown or grey; hyalite, a colorless glass opal, and many more.

Sources

Opals come primarily from Australian mines, but may be found in various parts of the world.

  • The largest amount of opal comes from various parts of Australia. 95% of the world’s opals are excavated from all over Australia. Coober Pedy, in South Australia, is the main source of opals. Mexico and Mesoamerica have common, water, jelly, and fire opals. The rare black opal is found in Lightning Ridge, New South Wales. Boulder opals have a main source in Quilpie, Queensland.
  • The United States also has mines that excavate white opals in Spencer, Idaho. These are used for making triplets and doublets.

Synthetic opal

Synthetic opals have a unique set of characteristics not seen on natural opals.

Opals have been synthetically made for both experimental and commercial purposes. In 1974, Pierre Gilson made the first synthetic opal; the material formed has distinct regularities (unlike natural opals) and its patches of color are arranged in 'lizard skin' or 'chicken wire' patterns. Synthetics lack in fluorescence, are lower in density and highly porous.

The two major manufacturers of imitation opals are Kyocera and Inamori of Japan.

Characteristics

Opals' displays of color, water content and purported mystical properties make them truly unique gemstones.

However, the quality of colors and varieties depend on the sources of these opals. Different sources have distinctive types of opals. If an opal is lacking in its display of colors, then it can be assumed that it is a common opal.

Opal is not very hard. It is only 5.5 to 6 on Moh's scale. Therefore it requires a protective setting.

Opals are highly recommended for overcoming depression. They also help to find true and real love. Consequently, opals are often worn by men. Moreover, it is believed that an opal’s changing colors may be compared with the changing emotions of a human being. It is therefore very important to wear the right kind of opal. Opals are like humans: the more 'experienced', the more different and renewed they become.