Opal is naturally found in a white coloured semi-precious gemstone composed of a silicate mineral family recognized for its marvellous ‘play of colours’. This astrological alternative of precious diamond is worn for gaining success in innovative pursuits, lavish lifestyle, social/financial prominence, matrimonial harmony and good health. Over thousands of years, people have quarried and treasured opals. These striking opal stones have energized a rich body of folklore. (Thus, opal gemstones have been considered both the luckiest and unluckiest stones one can wear).
Factual Information About Opal Gemstone
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Name |
Opal Stone |
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Varieties/ Different Names |
Agate Opal, Andean Opal, Black Opal, Boulder Opal, Common Opal, Crystal Opal, Cacholong Opal, Girasol, Fire Opal, Honey Opal, Hyalite, Hydrophane, Harlequin Opal, Jasper Opal, Matrix Opal, Moss Opal, Milk Opal, Pink Opal, Prase Opal, Precious Opal, Semiopal, Water Opal, White Opal Wax Opal, Wood Opal |
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Birthstone |
October |
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colour |
colourless, white, red (various shades), orange, yellow, yellowish brown, blue, black, grey, green, and violet. |
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Chemical Formula |
SiO2 · nH2O. Water= 1-21% in opal, generally 6-10% in precious opal. |
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Refractive Index |
1.37-1.47 |
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Hardness |
5.5-6.5 |
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Luster |
Vitreous, waxy, pearly. |
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Polish Luster |
Vitreous to resinous |
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Fracture Luster |
Waxy, sub vitreous |
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Fracture |
Conchoidal to uneven |
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Wearability |
Poor |
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Transparency |
Transparent to opaque |
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Luminescence |
Yes |
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Luminescence Present |
Fluorescent, Phosphorescent, UV-Short, UV-Long. Green fluorescence in opal commonly because of included U minerals. Much opal fluoresces strong white in SW, LW, with persistent phosphorescence |
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Enhancements/ Treatment |
Dyeing, Surface Coating, Infusion/Impregnation, |
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Care Instructions |
Heat sensitive, clean with room temperature soap and water. Avoid wearing gemstone or opal jewellery where it will get rough treatment. |
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Occurrence |
In sedimentary rocks or where low temperature solutions carrying silica can seep through rocks |
Assembled Opal Gems
A triplet from assembled opal gems adds a transparent quartz cap and makes for a good opal stone ring and opal earrings, since the hard quartz keeps the softer opal from scratching.
How to Determine Synthetic Opals?
Synthetic or lab-created opals are actually the real opals, but they’re grown in laboratories rather than yellowish-brown underground. They encounter the same formation processes, only at a stimulated rate in controlled settings.
Synthetic opals may exhibit an intense display of colour, generally in a mosaic pattern. With high magnification and backlighting, you can find a scale-like, snake skin or chicken wire structure in the pattern. When put under high magnification with transmitted light, synthetics may display a dendritic structure. Synthetic opals don’t phosphoresce (sparkle or twinkle) and may also stick to the tongue.
How to Detect Fake or Imitation Opal Gems?
Contrary to lab-created opals, imitations only simulate the physical look of opals. These imitations are essentially made from glass or plastic.
Plastic imitations or stimulants are soft and can be dissected with a sharp needle. They do not sparkle or twinkle (phosphoresce).
Glass stimulants essentially consist of glass bubbles and swirl marks. They also do not phosphoresce. Their refractive index (RI) and specific gravity (SG) are also generally higher than natural opal.
Care For Opal Stones
Nowadays, used frequently as opal necklace, opal rings and other opal jewellery, extra care of the delicate gemstone is well worth it. Highly sensitive to changes in temperature as well as a “crazing”, that implies they can easily form cracks or “craze” as they dehydrate, and must be kept cautiously.
Opals kept in water must be dried properly and cautiously before cutting.
Sometimes opals in rings can become chalky white and weary. This may owe to a network of scratches on the opal surface that dismantle the polish and dulls the colour play. However, a simple re-polishing can generally correct this. Having a hardness of only 5.5 makes them quite susceptible to scratching. Opals are thus usually not recommended for ring stones, unless the stone is positioned in a protective setting or a triplet for occasional wear.
Opal Stone Facts and Information
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Opal stone is sedimentary.
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Many ancient references to opal may actually indicate other gems, such as the iridescent iris agate.
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Under proper conditions, water seeps through the earth, becoming affluent in dissolved silicates. When water makes way through a cavity, it accumulates the silicates as microscopic spheres, forming opals.