Opal is the birthstone for October and the anniversary gemstone for the 13th year of marriage. The irony is that during the 19th century, opals were believed to be bad luck. This superstition is thought to have started with the writer Sir Walter Scott. In 1829, the heroine of his novel Anne of Geierestein owned an opal that burned fiery red when she was angry and turned ashen gray upon her death. This stigmatism prevailed, almost destroying the opal market until Queen Victoria finally dispelled the curse by giving opal jewelry as gifts at a royal wedding. The opal’s popularity grew, and in the early 1900’s the Diamond Commission resurrected this rumor because now opals were preferred over diamonds for engagement rings.
Opal is mainly from Australia, but it also comes from Mexico, Peru, Brazil and Indonesia. Australian opal comes in three varieties: Crystal Opal, Boulder Opal and Black Opal.
Black Opal is only found at Lightning Ridge in New South Wales, Australia. This magnificent gemstone is the most valuable form of opal. Its dark background color, usually black or gray, sets the spectral colors ablaze much like a storm cloud behind a rainbow. Black Opal is so valuable that even wafer thin slices are made into doublets or triplets to give them enough strength and depth to set into gold rings and other jewelry items.
Boulder Opal is found in several mines throughout Australia.The main ones are Coober Pedy, Andamooka and Mintabe. It’s very easy to distinguish Boulder Opal from other varieties; it always has ironstone on the back of it. Boulder opals are usually a blue/green color with sparks of red, yellow, orange or purple.
The third type of Australian Opal is crystal opal. It has a white body with a rainbow of complementary colors throughout. Crystal Opal is transparent and is pure opal (hydrated silica.) It typically has sharp clarity of diffracted color visible from within and on the surfaces of the stonel. When held out of the direct light, Crystal Opal displays some of the most intense color. This is the type of opal used in inlay jewelry, which has the base of the setting blackened before the precision cut crystal opal is set into it.
Opal is a fragile stone because all opals contain water. The content varies but it can be as much as 30%. Over the course of time, the stone loses water, cracks and the opalescence diminishes. This also makes the stones sensitive to pressure and knocks. Opal jewelry (and all other jewelry for that matter) should be put on AFTER using hairspray or perfumes, as the chemicals will break down the stone and cause it to lose its luster.
Opal's internal structure makes it diffract light; depending on the conditions in which it formed it can take on many colors. Opal ranges 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. Stones vary in optical density from opaque to semi-transparent. For gemstone use, a stone’s natural color is often enhanced by placing thin layers of opal on a darker underlying stone, like basalt.
Regardless of which type of opal you prefer, there is no other gemstone that displays such an intense array of colors and spectrums.