In the Orient, the opal symbolizes loyalty and hope. Arabs believed it came from heaven in flashes of lightning. The name “opal” is derived from an Indian word for “stone”
Opal is a hardened silica gel, usually containing 5-10 per cent water. It is therefore non-crystalline, unlike most other gemstones. The outstanding feature of precious opal is its opalescence, a rainbow-like iridescence that changes when viewed at different angles.
This iridescence is caused by the way the structure, a regular arrangement of tiny silica spheres, diffracts light – the larger the spheres, the greater the range of colors. Precious opal occurs in a number of color varieties:
Hydrophane opal- opal that becomes more transparent in water
Flash opal- opal with sudden flashes of brilliant color
Black opal- precious opal with a dark gray, blue, or green background that accentuates color play
Milk opal- opal with brilliant coloring on a white, milky background
Boulder opal- opal that is naturally attached to the rock it was formed in, which is of a different chemical makeup
Opal matrix- ironstone with thin veins or flecks of precious opal
Fire opal- transparent opal of red or orange, showing no flashes of color, it is often faceted
The most valuable opals will have a fantastic play of color without “dead” spots or “crazing” (internal fractures). Large pieces of good quality opal command high prices. Very thin pieces of opal are sometimes cemented to a backing of common opal or black onyx; this is a “doublet”.
These are not as valuable as regular opals of the same size, though they can be just as beautiful viewed from the top. When the opal is even thinner, a clear top layer of quartz is added to the doublet, creating a “triplet”.
Large deposits of opal are found in Australia. The staggering quantity mined there has completely eclipsed all other countries. Other places opal is mined are Mexico, Brazil, China, Guatemala, Honduras, Hungary, Japan, Czechoslovakia and the U.S.
Unlike its natural counterpart, created opal is much tougher and not prone to breakage. The brilliant colors are completely natural and not treated or enhanced in any way.
Opal is the birthstone of October.