Once categorized, opals are sold in price per carat or weight. Because there are so many opal fields in Australia, there really is no singular form of opal. When considering colors, a secondary and more complex layer of value emerges. The “dominant color” of an opal can affect its value, with red being the most expensive, followed by orange, yellow, green, blue, indigo and violet.
However, do not forget, a bright blue-green stone will be more valuable than a dull red one. The intensity of the colors is of paramount importance: the brightness of an opal is directly related to the price. The distinction and color these segments show determine the quality of an opal's pattern. For starters, precious opal, potch and common opal are mentioned in the first section of the nomenclature.
Gem cutters can take pieces of opal that are too thin to use as solid gemstones and assemble them into doublets and triplets. Opal is an amorphous form of silica, chemically similar to quartz, but containing 3 to 21% water within its mineral structure. Most opals, especially black opals, tend to form as ovals, and because opal is cut “cabochon” (with a domed surface), these features have traditionally been preferred for aesthetic and jewelry calibration purposes. Spectral colors (red, orange, yellow, green, blue, indigo, violet, in order of value) are generally combined in varying amounts in most opals.
Red (fire) opal is generally more valuable than a mainly green opal which, in turn, is more valuable than a stone that shows only blue color. By contrast, Ethiopia is a more recent source of opals, but some materials have been found to have a much higher water content, making it unreliable and potentially unsuitable for jewelry. The adjective solid has been removed from opal jargon for the simple reason that, from a scientific point of view, all varieties of opal are solid. Body tone refers to the relative darkness or luminosity of opal, while ignoring its play of colors.
The valuable opal is that it has a black background color; the color play contains shades that span the entire spectrum; the sparkles are large enough and evenly distributed throughout the gemstone; no inclusions or fractures. Thanks to Hatton Garden-based gemstone supplier, Marcus McCallum FGA, for taking these stunning photos of Ethiopian and Australian opals. Discovered around 1900 in Virgin Valley, Humboldt County, Nevada, opal presents itself here as cracks and joints in opalized wood. The term crystal opal refers to the 'diaphanity' (transparency) of an opal, not its crystal structure, and is defined as any type of opal that is translucent or transparent.
The particular colors seen in the fire of an opal depend on the size of the spheres and the angle of view.
