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Koroit opals.  Stones mined, cut, and photographed by the talented Gene McDevit at http://koroit.com/

I keep telling myself to shorten these Gemstones of the Week, but I found opal just too cool to abbreviate.

Pliny described opals like magical entities: “…for in them you shall see the living fire of the ruby, the glorious purple of the amethyst, the sea green of the emerald, all glittering together in an incredible mixture of light.”  Opals are mesmerizing gems, and a favorite of many, including myself.

However, popularity often leads to rumor, and opal has seen her share of tabloid headlines, sparked by ill-fated owners, hard times in history, and her delicate nature.  In Venice, opals worn by those stricken by the Black Death were said to flash brilliantly and then dull as the person succumbed to the disease.  In late 19th century Europe, it was considered so unlucky after its role in a novel that even royalty refused to wear it for fifty years.  Queen Victoria did much to bring her favored stone back into the markets (around the time the opal mines in her colony of Australia were forming, where the gem is not surprisingly considered very lucky).  In Asia it symbolizes hope and purity, and in the Middle East it is a protective charm from heaven, believed to have burst from lightning hitting the earth.  In Medieval Europe it had magic powers that could heal the eyes, as well as give its wearer invisibility and access to secrets.  For this reason it was called patronus furum, or the “patron of thieves”.  Blonde maidens in Scandinavia believed opal necklaces would keep their golden tresses from turning gray.

Opalized Plesiosaur skeleton articulated by Gondwana Studios for the National Opal Collection in Sydney.  Image from www.gondwanastudios.com.

Opal is a gel of silica crystals in water (SiO2.nH2O), from water trickling through silica and filling crevasses.  This usually occurs in sedimentary rock, similar to how fossils form, and there are stunning fossils that have become opalized.  Amazingly there are also opals created by plants.  Tabasheer opals, or “sugar of bamboo” in Sanskrit (also called bambusa in China and India), is a byproduct of certain species of bamboo absorbing silica from the soil, and is usually found rattling around in the nodes of the stalk.  The sweet, hard material is touted as a cough suppressant, antispasmodic, sleep aid, and aphrodisiac all in one.

Opal has been mined in many countries over the centuries, notably Hungary, Ethiopia, and Mexico, but today Australia is the source of 95% of our opals.  Australia is also the home of the many types of opal: black, white, jelly, crystal, fire, boulder, etc, each with its associated fun-to-say location.  As opals can contain 3-21% water, dehydration or sudden changes in temperature can cause an opal to break.  Due to their fairly soft nature (4.5-6 Mohs, about the same as glass), they are usually worn as earrings or pendants.  The size and uniformity of the spheres of silica crystals dictate the opal’s appearance, and the play of color is from the diffraction of light.  Crystals smaller than 1500 angstroms produce blue and violet colors, and crystals up to 3500 angstroms produce flashes of orange and red.  As opal is made of tiny crystals but does not have its own crystal structure, it is classified as a mineraloid and not a mineral.  It is still beautiful, and I am saving mine for some special pieces.