Opal | October Birthstone
Opal Stone | Facts and Photos
Opal along with tourmaline is the birthstone for the month of October. Stones fall into one of two categories, precious opal and common opal. The precious variety boasts an iridescence better known as "play of colour" which has been highly prized since Roman times whilst common opal lacks play of colour but can be found in many different colours. Play of colour is caused by the reflection and scattering of light from the minute uniformly sized and closely packed silica spheres within opal. Around ninety five per cent of the world's opals come from the outback deserts of Australia and the remaining five per cent are mined in Mexico, Brazil, the U.S states of Idaho and Nevada and more recently reserves have also been found in Ethiopia and Mali. The photograph above is a 54.7 carat Ethiopian stone that's currently on display in the Smithsonian National Museum of Natural History in Washington D.C.
Although first discovered by Australian gold prospectors in 1863 opal is believed to have been mined much earlier by the Aztecs in South and Central America.
Legends and myths have always been associated with gemstones and a story told by Australian aborigines claims that God came down to earth on a rainbow in order to bring the message of peace to all mankind and at the spot where his foot touched the ground, opals came alive and sparkled with all the colours of the rainbow.
The origins of the name possibly came from the Sanskrit word 'upala' meaning 'valuable stone' which in turn was probably the root for the Greek term 'opallios' meaning 'colour change'. The Ancient Greeks believed opals could give the wearer the power of foresight whilst the Romans revered them as a symbol of hope and purity and believed they could offer protection from disease. Eastern people regarded the stone as being a symbol of truth and the ancient Arabs believed it came from heaven and acquired its play of colour from flashes of lightning. During the Middle Ages it was thought to be beneficial for eyesight and some even believed it could render the wearer invisible hence opals were often carried by thieves. The French Emperor Napoleon gave his wife Josephine a magnificent stone called 'The Burning of Troy' named because of the variation of colour.
Natural History Museum of Los Angeles. Photo by Stan Celestian
A superstition brought about by the novel Ann of Geierstein written in 1829 by Walter Scott damaged opal's popularity because it was described as being an unlucky stone but its reputation was gradually restored by public figures such as Queen Victoria and the French actress Sarah Bernhardt.
More Opal Facts
Common opal which is not as well known or as popular as precious opal can be found in many different colours but the most highly sought after stones are pink and green. It's almost always opaque and the reason it's called "common" opal is because it can be found in many countries around the world. Like precious opal it's always shaped and polished as a cabochon.
Boulder opal is another type of stone which forms in thin veins within ironstone boulders. These are fine grained heavy and compact sedimentary rocks whose main components are the oxide of iron, clay and/or sand. Freshly broken ironstone is usually grey however the brown external appearance is due to the oxidation of its surface. Ironstone can also be found in a red and black banded form and when the mineral is polished as a gemstone it's better known as tiger iron.
Opal does not exhibit a crystalline structure therefore cannot be described as a mineral and is instead correctly known as a mineraloid or an amorphous (non crystalline) solid.
In crystal healing it's said to help with depression and to help the wearer to find true love. It can enhance the positive characteristics for people born under the zodiac sign of cancer. Precious opals are fragile and need to be well looked after. On Mohs scale of mineral hardness they grade 5½ to 6½ so should be protected whenever not being worn.
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Further ReadingFacts and Links on Wikipedia
More Information from Geology.com