Opal

October's fiery modern birthstone, the Opal has a long tradition of lore surrounding it. From the ancient Arabs believing that the opal received it fiery colors when it fell from the heavens in flashes of lightning to the modern-day alternative healers who believe the opal's colors and high-water content is able benefit a person's emotional and spirtual health, this gemstone seems to have never been without mystical and mythical properties associated with it.

In direct contrast to its ancient and more modern lore, the Opal's reputation suffered during the European Black Plague in the fourteenth century. The opal was supposed to lose its luster--its fire--when its owner died of the plague.

Unlike other minerals, opal never really forms crystals. Indeed, opals always contain water, from three-to thirty percent of an opal is made up of trapped water. Most gem-quality opals have between three and six percent water. A loss of water because of heat or excessively dry storage conditions will cause an opal's play of color to diminsh.

Opal forms when silica-rich liquids solidify in cavities to form nodules, crusts, veinlets and masses. Opals can form in crevices in volcanic rock, around hotsprings, or replaces wood during fossilization.

Up until the end of the 19th century, easter Slovakia provided the world with the best qualities of opal. Today, the overwhelming majority of gem-quality opal comes to us from Australia. Famous deposits of opal in Australia include Lightning Ridge and White Cliffs in New South Wales and Coober Pedy and Andamooka in Southern Australia.

The Opal is divided into three subgroups: the Precious Opals, the Yellow-Red Fire Opals and the Common Opals.

Precious Opal
The special characteristic of these gems is their play of color, a display of rainbow-like hues. These colors change with the angle of observation.

Black Opal is the most rare and valuable type of opal. Black opal has a dark underlying body color--dark gray, dark blue, dark green, gray-black--which gives greater intensity to the opal stone's play-of-color.

Boulder Opal is a precious opal with a dark base surface, color-play, and occurs in pebble rock, where opal fills hollows. Boulder opal is only found and mined in Queensland. The gem is found in a matrix or surrounding rock called ironstone or dark brown sandstone.

Crystal Opal is precious opal that is transparent with a strong color-play on a colorless, vitreous surface. Crystal opal can be extremely beautiful. Although Lightning ridge is most famous for black opal, it also produces exquisite light and crystal opal.

Harlequin Opal is precious opal that is transparent to translucent and has mosaic-like color patterns.

Precious Opals are often fused with other materials during the cutting and polishing process, resulting in a Doublet or Triplet Opal.

A Doublet is made by fusing a dark backing, to the back of the gem opal, producing a double layered gem with an appearance similar to black opal.

A Triplet is similar to a doublet except that the slice of gem opal is very thin, and a third layer, usually a layer of tanspaent material e.g. a domed piece of hard plastic or quartz crystal is added to the top of the gem.

Fire Opal
Fire Opal--named after its bright orange color--often shows no play-of-color. Most Fire Opal is milky, but the most sought-after speciments are clear and transparaent and therefore able to be facetted. The Fire Opal from Mexico is probably the best known, however it can also be found in the United States, Brazil, Guatemala, and Western Australia.

Common Opal
Common Opal is indeed common and prevalent. It is opaque, exhibits little or no display-of-color. Common Opal is a dull yellow, white, red, or black color and is used in industry as an abrasive or a filler.