Opal Value, Price, and Jewelry Information
Varieties
The term “common opal” refers to opaque or glassy opals with a waxy luster. These stones come in a wide range of colors. They are seldom cut. Common opals are often fluorescent.
The term “precious opal” refers to opals of any color that display fire or a play of colors. They are also sometimes referred to as “noble opals.”
* Black opals have a black body color with fire, which is often spectacular against a dark background. Body colors can also be very dark blueish, greenish, or brownish. The name is also applied to black potch (inferior opal material) covered with a thin layer of crystal opal, which lets the black later show through.
Black Opal, Australia, lighting position #1 (Stone in Ring ~ 10 carats)
* Gray or semi-black opal has light to dark body color with fire.
* White opal has a white body color with fire.
* Water opal has a transparent or colorless body that may have fire in it.
* Crystal opals are colorless and transparent to semi-transparent in transmitted light but with a rich play of colors in reflected light. Black crystal opals are transparent to semi-transparent with dark body color and play of color.
* Milk opal is translucent, milk white opal. These stones may also be yellowish or greenish in color.
* Fire opal is translucent to transparent with a yellow, orange, or red body color. These stones may or may not display a play of colors. The “fire” in their name refers to their body color, not to play of color. These stones are also called Mexican or sun opals.
* Boulder opals are thin seams of opal that form in ironstone. These opals come in many colors and show dazzling fire, backed by their brown ironstone matrix.
* Contraluz opals are very rare. They are usually found in Mexico but have also been found in Australia. They are transparent opals and show a play of color in both transmitted and reflected light.
Opal, Contraluz, Mexico, illuminated from front (~ 4)
* Hyalites are transparent to translucent, colorless or white to gray opals with glassy luster. They have little to no play of color. They are rarely faceted but generally have no gem significance. They are also called jelly opals.
* Moss opal is white to brownish and opaque. They contain dendritic inclusions that resemble moss.
* Hydrophane opals are light colored and opaque. When soaked in water or oil, they become transparent and show a display of color. They are sometimes called “magic stones.”
* Siliceous sinter or geyserite is glassy opal that forms around hot springs and geysers. These massive formations are not faceted for jewelry.
* Tripoli or diatomaceous earth are fine-grained, powdery masses of opal or the siliceous remains of microscopic marine animals called diatoms. This material is often used in polishing agents and fillers.
* Cachalong opal is porcelaniferous. (It resembles porcelain). It’s often blueish-white, translucent to opaque, and very porous. It will stick to your tongue. This stone is also called kalmuck agate opal.
* Jasper opal is reddish-brown and opaque. It resembles jasper.
* Prase opal is a green to yellowish green, translucent to opaque, common opal. It resembles chrysoprase. A golden-green variety is called chrysopal.
* Menilite is an opaque gray to brown opal with a concretionary structure.
* Tabasheer is an opaline (opal-like) silica found in the joints of some bamboo.
* Girasol opal is semi-transparent to translucent with a moving, billowy light effect. It resembles moonstone.
* Chrysocolla opals get their blue color from finely disseminated inclusions of chrysocolla, a copper phyllosilicate mineral.
* Liver opal is a term sometimes used for brown, common opal.
* Resin opal is a yellowish brown common opal with a waxy to resinous luster.
* Iron opal is a red to yellow common opal.
* Louisiana opal is composed of quartz, opal, and pyrite. It is found in the state of Louisiana.
* Oolitic opals have small black or brown spherical inclusions resembling fish roe and an over play of color.
* Wax opal is yellowish with a waxy luster.
* Star opals are extremely rare. The asterism they display is caused by imperfections in the arrangement of their silicate spheres, unlike the star effects of other gems such as sapphires, which are caused by inclusions.
https://www.gemsociety.org/article/opal ... formation/