What is Opal
Opal is a noncrystalline form of silica containing varying amounts of water, usually 3 to 10 percent. Opal forms as a low-temperature deposit around hot springs, often embedded in sandstone. Large deposits of opal are found in Australia. It is also found in Brazil, Guatemala, Honduras, Indonesia, Japan, Mexico, Peru, Russia, and in the U.S. (Nevada and Idaho).
Light illuminates the inclusions of microscopic drops of water and creates the iridescent phenomena known as play-of-color. The rainbow-like hues change with the angle of observation and each opal is unique.
Opal Color and Characteristics
Opals may be treated to enhance their body color and make the play-of-color more vibrant. Smoke-treating and Sugar-treating involve changing an opal with a white body color to a dark body color to make the play-of-color stand out in higher contrast. Opals may also be treated by saturation with wax, oil, or epoxy to prevent or disguise cracking.
Experts divide opals into several major groups:
White or light opal: Translucent color, with play-of-color against a white or light gray background color.
Black opal: Translucent to opaque, with play-of-color against a black or other dark background.
Fire opal: Also known as a Mexican opal. Transparent to translucent, with brown, yellow, orange, or red body color. May or may not exhibit play-of-color. Generally faceted like a gemstone.
Boulder opal: Translucent to opaque, with play-of-color against a light to dark background. Fragments of the surrounding rock, called matrix, become part of the finished gem.
Crystal or water opal: Transparent to semitransparent, with a clear background. This type shows exceptional play-of-color.
Jelly opal: Bluish-gray with little play-of-color.
Harlequin opal: Transparent to translucent opal with effective mosaic-like color patterns.
Softer and more fragile than other gemstones, opal requires special care when worn. Opals have high water content and tend to dry out causing them to craze. Avoid storing your opals in airtight areas, such as a safety deposit box. The dry climate tends to accelerate the drying of an opal. Additionally, heat and sudden temperature changes may also cause opals to crack, so they should not be put into an ultrasonic or steam cleaner. Should your opal become soiled, you should clean it with a soft cloth. It is important to have your jewelry professionally cleaned and checked three to four times a year. When not worn, opal jewelry should be stored in a jewelry box lined with soft fabric.
Common shapes for opal include oval, pear, and marquise. Most opals are cut into a cabochon, they are not faceted. Fire opals are the exception and are generally faceted like other colored gemstones. With a variety to choose from you can find opal jewelry to fit any style or ocassion such as October birthdays.