Opal could be considered the most colorful of gems. The wide range of color displays is unsurpassed. The best quality opals can sometimes be more valuable than diamonds. Opals, which display colors, are known as precious opals. Opals, which lack the colored sparkle of the precious opals, are referred to as common opals. Gems are cut from both types but the precious forms are most often used in jewelry. The most desirable of all opals are the black opals. "Black" may be a bit of a misnomer because the background colors can range from dark blue to dark green to black and most have colorful sparkles in them.

Opals are largely mined in Australia. However, blue precious opal is mined in Arizona; several varieties are mined in Idaho; precious opal is mined in Nevada; and very fine quality opals are mined in Oregon.

The name, Opal, is believed to have evolved from the Greek word, opallios, meaning change of color. Greeks believed opals gave their owners the powers of foresight and prophecy. Romans on the other hand, regarded opals as a token of hope and purity. In Twelfth Night, Shakespeare referred to opal as "the queen of gems." Arabians believed they fell from heaven.

Opal has a hardness value of 5 ½ to 6 ½. Opals often crack when left to dry out too quickly, due to their high water content. But if made to dry out slowly, over a period of months or years, they can sometimes be stabilized to avoid the common cracking. Likewise the stones are relatively soft and need to be treated with respect to avoid chipping them.

Opals are often used in rings, earrings, pendants and pins.

Sometimes opal doublets are used in jewelry. These are thin slices of precious opal, which are glued onto a matrix material. These forms of opals are much less expensive but still very beautiful. Most often these doublets are coated with a thin layer or dome of clear quartz to make them more resistant to scratches and these are referred to as triplets.

Scientists have become highly skilled at creating laboratory opals. These synthetic opals have been on the market since 1974. These are not simply look-alikes, these are made exactly of the same materials nature uses and the structure is perfectly reproduced.

Opal is sensitive to heat and it would be very unwise to come in out of the cold and suddenly plunge it into hot water.

Opal is the birthstone for October. For a time it was believed unlucky to wear opal if it wasn’t your birthstone. This rumor is believed to have started after the publication of a novel by Sir Walter Scott, Anne of Geierstein. In it the heroine owned an opal which burned red when she was angry and turned ashen gray when she died. Queen Victoria helped dispel the rumor by giving opals as wedding presents.

Opals are believed to help the wearer to see the broader view of things. Some believe they help clarify things by amplifying and mirroring feelings. Opal is said to help uncover buried emotions and reveal the deepest desires of love and passion. Some opal wearers believe they feel less inhibition and more spontaneity. Fire Opals are said to stimulate energy, but beware, it’s also believed to cause flares of temper and fits of passion.