Opal is an extremely precious gem. Here, the manager of Gem-A Instruments, Samatha Lloyd FGA EG, provides a quick but essential guide to the value factors of opal and what distinguishes a fantastic specimen from an average one. There are a number of factors that alter the value of opals. As mentioned, black opal may have higher prices than light opal (especially with a tinted black body tone), although this is not to say that a fantastic light opal can't be more expensive than a mediocre black opal.
Opals that have a rare or unique pattern are more valuable. The harlequin pattern is the rarest and most loved pattern in opals, but it is very rare. A true harlequin pattern is a wide mosaic pattern, set of angular colors. Floral patterns are sometimes called floral harlequin.
Opal is an amorphous form of silica, chemically similar to quartz, but containing between 3% and 21% water within its mineral structure. Gem-grade opals typically have a water content of 6% to 10%. And there's a whole epic story of why there should be opal there, and you go and dig there, and it's not. For example, black opal gets its color from volcanic ash, but inclusions have nothing to do with the play of colors.
Black opal is one of the most charming stones in the world, sought after for its seemingly infinite display of colors. Valuable opal is the one with a black background color; the play of colors contains shades that span the entire spectrum; the sparkles are large enough and are evenly distributed throughout the gemstone; no inclusions or fractures. Hyalites or jelly opals are transparent to translucent, colourless or white, with a vitreous sheen and little or no play of colors. Some opals will have a vegetation pattern from inclusions and this is popular since opal has replaced part of the tree or vegetation.
Though once known as “bad luck”, opals are quickly becoming one of the most sought-after gemstones in jewelry collections. Usually, opals with a black or dark body tone are more valuable than those with a white, light or crystalline body tone, because a stone with a darker body tone tends to display colors more vibrantly. This common variety of opal comes in green, lavender or purple colors and can also show a cat's eye. The Opal Shine Guide was produced by the Australian Opal Association together with the body tone guide.
As opals grow by filling cavities in the earth, they sometimes take the form of pieces of wood, bones and seashells buried in the ground. This opal has a mosaic of strong colors and looks very attractive against a milky white background color. Oval stone is generally considered more valuable than free-form, except with rock opals where free-form is considered desirable. Boulder opal, for example, usually has a very thin color bar due to the way the opal is geologically formed.