10 Interesting Facts About Opals

Illustration of opal jewelry on a table
The Spruce / Melissa Ling
  • 01 of 11

    Opal Facts

    Uncut opal
    David Wall Photo / Getty Images

    Opal is arguably the most unique, diverse, and beautiful birthstone. Unlike most gemstones, opal is amorphous which means it does not have a defined crystalline structure. It takes on many shapes and colors and in that way, it is pretty unpredictable.

    Opals are very interesting and there are some myths that you'll want to know about as well. We even have some spectacular specimens for you to admire as you learn about this fascinating gemstone.

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  • 02 of 11

    Ancient Gemstone

    Opalized fossil
    Harry Taylor / Getty Images

    Opals have been the muse of artists, writers, and other creatives since what seems like the beginning of time. The exact origin of opal's name is disputed, but historians are confident that in ancient Rome opal was known as opalus which translates as the "precious stone."

    Was the opal the ancient Romans admired the same as the one we admire today? No one is sure. However, evidence of opal artifacts date as far back as 4000 B.C.

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  • 03 of 11

    Opal Development

    Closeup of opal specimen
    aleskramer / Getty Images

    Not only has opal been in the minds and hearts of mankind for hundreds, if not thousands, of years, opals take a very long time to form.

    Though the exact cause of opal formation is still disputed, many believe that silica was carried down into rock crevices by heavy rains. Once the water evaporated, what was left was a silica gel that then hardened over the course of what some believe is millions of years. This didn't happen overnight! It takes roughly 5 million years to solidify just one centimeter of opal.

    This theory makes sense considering opal has water in it. The water content of an opal can be upwards of 20 percent but is usually in the 5 percent range.

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  • 04 of 11

    Origins and Types

    Brightly-colored opal from South Australia
    John Sones Singing Bowl Media / Getty Images

    It is estimated that nearly 95% of the world's opal comes from Australia. Other countries that commonly mine opals include Ethiopia, Brazil, and Mexico.

    There are two types of opals: precious and common. Precious opals either have vibrant color (fire opal) or exhibit a play of color. Play of color is a term coined to describe the unique multi-dimensional color display that the more precious opals have.

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  • 05 of 11

    Opal Colors

    Close up of uncut opal specimen
    Dorling Kindersley / Getty Images

    Precious opals have two basic colors, their background color and their play of color. The background color is caused by impurities within the silica. Within the precious opal family, there are many different varieties of opal. Each has their own unique color combinations and character traits. Opals can be found orange, yellow, red, green, blue, or purple. Black opals are considered one of the rarest gemstones, though they too can be a variety of dark colors.

    The other colors are caused by the way silica forms together. Silica is composed of a bunch of tiny spheres that adhere to one another. When they fuse, tiny gaps are created between them that allow the light to diffract. This diffraction causes a magnitude of different shapes and color combinations.

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  • 06 of 11

    Price of Opals

    Fancy boulder opal closeup
    Wilson Valentin / Getty Images

    Unlike many other gemstones on the market, opals are usually left in their natural state. However, some common treatments include fracture filling and smoke treatment, which is used to darken the stone.

    Opals that have the most intense and diverse play of color are generally the most expensive and prized. Boulder opal is the only opal that can display the entire rainbow within one stone. That's at least seven colors if you count indigo.

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  • 07 of 11

    Synthetic Opals and Doublets

    Closeup of a rough opal
    Oliver Gerhard / Getty Images

    Opals have been synthesized since the 1970s. Natural opals have also been sliced and adhered to onyx and other gem material to give the illusion of a bigger, dark, more expensive opal. The "doublets" are more susceptible to harm if they are submerged in liquids for long periods of time.

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  • 08 of 11

    Hardness of Opals

    Cut Australian opal
    Sun Chan / Getty Images

    Opals rank 5.5 to 6.5 out of 10 on Mohs Scale of Hardness. They are certainly more fragile than the other birthstones, so you do need to be careful with them. However, with proper care, they should hold up well.

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  • 09 of 11

    Opal Gifts

    Oval-shaped cut opal gemstone
    alicat / Getty Images

    Opal became the official birthstone of the month of October in 1912. The National Association of Jewelers came together at that time to finalize the longtime debate as to which gemstones represented each month. Opal has been a clear winner for the month of October since the 15th century.

    Not only is there a birthstone from every month, there are Zodiac birthstones as well. The birthstones that apply to your Zodiac sign are not as defined as the monthly birthstones that were cemented by the National Association of Jewelers.

    Many cultures throughout history have associated different gemstones with astrological signs. The stone that aligns with your sign largely depends on which list or culture you choose to follow. Opal has commonly been associated with the signs Scorpio and Libra, which aligns with October.

    Opal is also the official gemstone gift alternative for the 14th wedding anniversary.

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  • 10 of 11

    Bad Luck

    Cut and polished opal gemstones
    Science Photo Library - LAWRENCE LAWRY / Getty Images

    Many people believe that wearing an opal if it is not your birthstone or buying an opal for yourself is bad luck. There are many stories of opals getting lost or destroyed and the owner blaming the occurrence on this superstition. One reason the superstition may have developed is due to the fact that opals are a softer stone and more susceptible to damage.

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  • 11 of 11

    Petrified Wood

    Precious opal, rough specimen
    Gary Ombler / Getty Images

    Petrified wood or "fossil wood" has the same makeup as an opal: amorphous silica. However, not all petrified wood is considered opal. Sometimes, however, the fossil can be overtaken with an opal-like sheen or be replaced with opal entirely.