Opal Education
What is an Opal?
Opal is a hydrated amorphous form of silica. Unlike most gemstones, opal is non-crystalline, meaning it lacks a defined crystal structure. Its internal structure is composed of tightly packed microscopic silica spheres. When light passes through these spheres, it diffracts, causing the mesmerizing "play-of-color" that opals are famous for.
Types of Australian Opals
Black Opal
The most valuable type, mined primarily in Lightning Ridge. It features a dark body tone which makes the colors pop.
Boulder Opal
Mined in Queensland, these opals form within ironstone boulders. The ironstone is left on the back for strength and contrast.
Crystal Opal
Transparent to semi-transparent opals. Mainly found in Coober Pedy. Incredible when held up to the light.
White/Light Opal
Features a light or white body color. The more common type of opal, offering delicate pastels.
Valuing an Opal
Opal valuation is complex. The most critical factor is the brilliance of the color, followed by the pattern (Harlequin is the rarest), the body tone (darker is generally more valuable), and the size (carat weight). A highly brilliant crystal opal can sometimes be worth more than a dull black opal.