All About Opal

“And lo! the beautiful opal – That rare and wondrous gem – Where the Moon and Sun blend into one is the child that was born to them.” – poet Ella Wheeler Wilcox

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Marianne Hunter Kabuki Kachina brooch utilizing several different types of opals with gold and enamel

What causes the spectacular display of color in opal?

Opal is comprised of hydrated silica spheres. The silica in opal have no definite crystal structure. This technically makes opal a mineraloid and not a mineral. But hey – who’s counting? What gives opal its display of color is how light interacts with these silica spheres. These spheres are very uniform in size and are tightly packed either in a cubic or hexagonal shape. The interference and diffraction of light caused by these tightly packed spheres are what causes such spectacular color displays.

Precious White Opal – Perhaps the most ubiquitous and what most people think of as opal. This type of opal hails mainly from Australia, the best quality coming from the Coober Pedy mine. Some show spectacular play-of-color, red, being the most coveted in the rainbow of colors displayed. Trade terms for the color patterns such as ‘pin fire’ or ‘harlequin’ are often used to describe them – generally large patches of many different colors are preferred over small dots or displays of only one or two colors.

Precious Black Opal – Black opal have all the same properties as white opal but has a dark background body color (usually in varying shades of gray or blue) which lends very well to showing off the rainbow color patterns. The color red against a black background is very desirable and commands high prices. Beware of treated black opals – treatments range from ‘smoking’ white opals to darken the body color.

Boulder Opal – Another natural wonder of Australia . . .  Opal material (hydrated silicate spheres) seeps into cracks and fissures in a host rock during formation millions of years ago creating an array of spectacular scenes. A common host rock seen in many boulder opals used in jewelry is the Queensland ironstone. Below is a rare carved boulder opal in a Elizabeth Gage necklace and an unset boulder opal with Queensland ironstone matrix.

Doublet Opal – A doublet is made up of a thin layer of precious opal epoxied onto a backing material (usually Queensland ironstone) which gives it durability and strength. This is a wonderful way to get the ‘look’ of precious opal without incurring the prohibitive cost of a solid high quality opal. Once a doublet is bezel set, the ironstone layer will never be seen again leaving only the gorgeous precious opal visible. Some opal doublets are absolutely spectacular in their own right and should not be seen as an ‘imitation’ or an ersatz opal.

Ethiopian Welo Opal  – This is a relatively new find. These opals have a ‘watery’ appearance and show intense play-of-color on translucent (usually yellowish), black or even clear body color. They react in interesting ways with water . . . if you put one in water, the opal could become completely clear either intensifying the play-of-color or making it disappear all together. Once the opal dries out, it will revert back to its original appearance. When making a purchase of Welo opals, make sure that the opal is completely dried out so that you’re seeing the opal as it is meant to be ensuring you won’t be in for a surprise in the future.

Fire Opal – Fire Opal is an intense orange colored opal. Displaying no play-of-color, it is technically a ‘common opal’, however, this fiery gemstone is far from common! In large sizes, this gem is very rare. The most coveted color is an orangey red hue resembling the flesh of blood oranges. Believed by the ancients to be the utmost expression of passion and love, the highest quality fire opal is magnificent.

Common Opal – Common opal by definition simply means that these opals display no play-of-color. So, any solid color opal, whether transparent, translucent, opaque or somewhere in between is a common opal. A popular variety of common opal is known as Peruvian opal. This typically refers to a very specific shade of opaque pastel pink and seafoam blue/green opal. Other colors for common opal are yellow and white.

images via Sotheby’s, opalauctions.com, Irene Neuwirth, Mariane Hunter

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