Opal is the birthstone for October and the 18th anniversary. It’s name is derived from the Greek Opallos, meaning “to see a change (of color).”
Because opal has the colors of other gems, the Romans thought it was the most precious and powerful of all the gemstones on Earth.
Many cultures have credited opal with supernatural origins and powers. Arabic legends say it falls from the heavens in flashes of lightning.
The ancient Greeks believed opals gave their owners the gift of prophecy and guarded them from disease. Europeans have long considered the gem a symbol of hope, purity, and truth.
Some people think it’s unlucky for anyone born in another month to wear an opal. But that particular superstition comes from a novel written in the 1800s (Anne of Geierstein by Sir Walter Scott), and not from any ancient belief or experience.
In fact, throughout most of history, opal has been regarded as the luckiest and most magical of all gems because it can show all colors.
Opals range in color from milky white to black with flashes of yellow, orange, green, red, and blue. An opal’s beauty is the product of contrast between its color play and its background.
Opal is a formation of non-crystalline silica gel that seeped into crevices in the sedimentary strata. Through time and nature’s heating and molding processes, the gel hardened into the form of opals.
During dry periods, much of the water evaporated, leaving solid deposits of silica in the cracks and between the layers of underground sedimentary rock. The silica deposits formed opal.
Play-of-color occurs in precious opal because it’s made up of sub-microscopic spheres stacked in a grid-like pattern. As the lightwaves travel between the spheres, the waves diffract, or bend. As they bend, they break up into the colors of the rainbow, called spectral colors. Play-of-color is the result.
Although experts divide gem opals into many different categories, five of the main types are:
White or light opal: Translucent to semi translucent, with play-of-color against a white or light gray background color, called bodycolor.
Black opal: Translucent to opaque, with play-of-color against a black or other dark background.
Fire opal: Transparent to translucent, with brown, yellow, orange, or red bodycolor. This material—which often doesn’t show play-of-color—is also known as “Mexican opal.”
Boulder opal: Translucent to opaque, with play-of-color against a light to dark background. Fragments of the surrounding rock, called matrix, become part of the finished gem.
Crystal or water opal: Transparent to semitransparent, with a clear background. This type shows exceptional play-of-color.
Opal is typically untreated, but it may be impregnated with oil, wax, or plastic to enhance color and stability. It may also be layered (as in doublets or triplets) for durability.
‘Smoking’ treatments are now more common than before. ‘Smoking’ of opal is done to darken body color which enhances play of color, most often seen with Ethiopian opal.
Opals are delicate gemstones. Their most significant weakness has to do with their water content. If an opal is allowed to dry, it will crack and fade.
If you live in a very dry climate, or keep them in a dehumidified room, some precautions are necessary. Keeping them in a tight plastic bag, with a damp piece of cotton or fabric will prevent dehydration.
Because of their water content, opals are also highly sensitive to sudden changes in temperature.
Being somewhat soft, opals scratch easily. It is important to realize that a large component of ordinary dust is quartz which has a hardness of 7-7.5. At 5.5 to 6 in hardness, simply wiping the dust off an opal will gradually reduce its polish.
The solution is to clean your opals using a soft cloth and only mild soap or detergent if needed. Do not use harsh chemical or cleaners and avoid ultrasonic cleaners and steamers.
Always remove opal jewelry before engaging in vigorous physical activity.
We hope this article has given you a bit more of a background on opals, but should you have any additional questions about this or any other jewellery related topics, you can always: “Ask the Jeweller”
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