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What Are the Uses of the Mineral Opal?

The mineral opal is not used industrially but has great value as a gemstone. In scientific terms, opal is considered a mineraloid because the structure is not truly crystalline. Opals are heat-sensitive, break easier than other minerals and must be stored in damp, cotton wool to avoid brittleness, according to the U.S. Geological Survey. These characteristics, however, do not detract from their value as a colorful gemstone that can be worth more than diamonds. Opals contain oxygen and silica, which give them an opalescent beauty through diffracting light.

Religious Practices
- Opals have a hardness factor of 5.5 to 6.5 on the Mohs scale.
  
  Throughout history, opals were thought to give their owners certain powers. The early Greeks believed that opals gave their owners the gifts of foresight and prophecy. Romans believed that opals were tokens of hope and purity, and Arabs believed the gems fell from heaven, the U.S. Geological Survey reports. People have admired fire opals since ancient times, and they were used in religious practices of the Mayas and Aztecs in Central America and Mexico. Starting in the 19th century, superstition began to follow the opal. Some people believed that it was bad luck to carry or wear a opal if it was not the owner's birthstone. This superstition eventually diminished.
Jewelry
- Opals must be kept in humid storage to prevent dehydration and cracking.
  
  The opal's primary function is as a gemstone. Precious white, black and fire opals are cut into cabochons and set into jewelry. Opal rings, bracelets, earrings and necklaces are highly desirable and can be costly. Black opal is the most valuable variety, and quality specimens are known to surpass the value of diamonds, reports opalglobe.com. Black opals contain carbon and iron oxide, two elements missing in other opals. Varieties used in jewelry also include crystal and boulder opals. Boulder opals, the second most valuable variety, are found only in the ironstone boulders of Queensland, Australia.
Mineral Collecting
- Fluorescent opals come in a variety of colors.
  
  Opals that have bright, fluorescent characteristics are popular with fluorescent mineral collectors, who often break or saw the fluorescent skin on the opal's surface (usually pink or blue-green) to show a mix of colors under a fluorescent lamp. Green fluorescent opals have been found in New Jersey, and Wyoming is home to blue, green and pink varieties. Orange, tiger-striped fluorescent opal varieties have been found in Nevada.

Rocks & Minerals