October is for Opals; Buying and Caring for Them!
Opals are October’s birthstone (and a suggested gift for 14th wedding anniversaries). They’re also the national gemstone of Australia, the country that supplies the majority of these gems throughout the world. They’re an attractive and fascinating stone. The Romans thought opals were the most precious and powerful of gems, because they encompassed all the colors of other gems in one.
An opal takes millions of years to form. A member of the quartz group, each one is unique, with a separate and distinct shine and sparkle from a continuously changing play-of- colors.
The colorful stones can take on hues from white to gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown and black. Red on black is the rarest, with white and green being the most common. The origin of the opal’s play-of-color, long a mystery, was discovered in the 1960s, with the aid of an electron microscope. The tiny silica spheres that compose an opal can be arranged in an orderly pattern that diffracts the light entering the stone into spectral colors. The density and pattern of the aligned silica spheres are responsible for the different colors refracted in the opal; it’s scintillation. Broad patterns (large flashes of color) are more valuable than pinfire and small patterns. Distinct patterns are rare, and include harlequin, rolling flash, jigsaw, block and ribbon.
The vibrancy of an opal’s colors is directly related to its value. Dominant colors, in value order, are red, orange, yellow, green, blue, indigo and violet.
Most opal gemstones are cut and polished to form a cabochon; a stone with a convex top and flat bottom. They often have an elliptical (oval) or other softly domed shape. Fire opals can be facet cut. The stone is best suited to jewelry crafted as rings, pendants, brooches and earrings.
Caring for Opals
Since opals are neither a hard nor tough stone, they should be treated with care. A few tips:
Types of Opals
Black Opal – Dark gray body with brilliant play-of-color; the most rare and expensive of opals. The brighter and sharper a black opal’s colors, the more costly it will be.
Boulder Opal – Transparent to opaque stone with play-of-color on a light to dark background. Formed naturally on ironstone rock, its fragments of the surrounding rock (the matrix) become part of the finished gem.
Crystal (Water) Opal – This transparent to semi-transparent stone with a clear background shows exceptional play-of-color.
Doublet – Frequently used for mass produced jewelry, this is a combination of an opal slice backed with a matching slice of the stone’s matrix or other material (onyx, obsidian, black glass).
Fire Opal – Brown, yellow, orange or red body color.
Triplet – The same as a doubled, with the addition of a layer of protection on top of the stone.
White/Milky – This translucent to semi-translucent stone shows more diffuse colors against a white or gray body color. Opals of this type are the most common and least expensive of opals. The stones often display red, green and blue pinfire.
Opals have had a rich, varied folklore. Dubbed the “Queen of Gems” by the ancient Romans, they’ve been considered a talisman, patron stone of thieves and the bearer of bad luck, and revered as a symbol of hope, fidelity and purity. Queen Victoria had an impressive collection of opals, and wore them throughout her reign. Additionally, the gemstone was celebrated throughout the Art Nouveau and Art Deco movements in the early 20th Century.
Among the world’s famous opals:
- Addeman Plesiosaur – This is the finest known opalised skeleton on earth.
- Andamooka Opal (also known as the Queen’s Opal) – A cut and polished 203-carat opal that was presented to Queen Elizabeth II on the occasion of her first visit to South Australia. It displays reds, blues and greens.
- Flame Queen Opal – This triangular-shaped opal is the best-known example of “eye-of-opal,” an eye-like effect created when an opal in-fills a cavity. Its flat central raised dome flashes red or gold, depending on the angle of view, with a band of deep blue-green surrounding it.
- Galaxy Opal – Listed as the “World’s Largest Polished Opal” in the 1992 Guinness Book of World Records, the finished piece, in the shape of a child’s head, weighs 3,749 carats.
- Halley’s Comet Opal – The world’s largest uncut black opal
- Olympic Australis – This stone is noted to be the world’s largest and most valuable gem opal ever found.
- Robling Opal – This 2,585 carat black opal with flashes of blue and green play-of-color, is at the Smithsonian Institution.
- The Burning of Troy – This black and red stone with a hit of green at the very edge was presented to the Empress Josephine by Napolean. Currently lost to public record, it was the first named opal.