Opals

Opals are formed from a mineral gel which is deposited at a relatively low temperatures and may occur in the fissures of almost any kind of rock, most commonly found with sandstone and basalt.

Precious opal shows a variable interplay of internal colors and Opals range in color from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the reds against black are the most rare, whereas white and greens are the most common.

Opal is Australia's national Gemstone and produces around 97% of the world’s opal. 90% is called ‘light opal’ or white and Crystal opal, 8% is black and only 2% is boulder opal.

The Virgin Valley opal fields of Humboldt County in northern Nevada produce a wide variety of precious black, crystal, white, fire, and lemon opal. The Black Fire Opal is the official gemstone of Nevada. The largest black opal in the Smithsonian Institution comes from the Royal Peacock opal mine in the Virgin Valley.

Another source of white or creamy opal in the United States is Spencer, Idaho. Spencer has an open pit mine that you can visit for a fee, about 4 times a year. One business in Spencer also brings material down from the mine site to their store, so that would be opal miners can dig for their own opal, again for a nominal fee.

The veins of Opal displaying the play of color are often quite thin, and this has given rise to unusual methods of preparing the stone as a Gem. An Opal doublet is a thin layer of Opal, backed by a swart mineral such as ironstone, basalt, or obsidian. The darker backing emphasizes the play of color, and results in a more attractive display.

Combined with modern techniques of polishing, doublet Opal produces similar effect of black or boulder opals at a mere fraction of the price. Doublet Opal also has the added benefit of having genuine Opal as the top visible and touchable layer, unlike triplet Opals.

The triplet-cut Opal backs the colored material with a dark backing, and then has a domed cap of clear Quartz or plastic on top, which takes a high polish and acts as a protective layer for the relatively fragile Opal itself.