Opal
Monday, October 5th, 2009
Arabic legend says opal fall from the heavens in flashes of lightening. The Greeks believed opals gave their owners the gift of prophecy and guarded them from disease. The Romans thought opal symbolized love and hope. The Romans gave its name – opalus – that meant precious stone. Europeans have long considered the gem a symbol of hope, purity, and truth. Australian aborigines have a legend that the creator came down to Earth on a rainbow to bring the message of peace. At the spot his foot touched the ground, the stones became alive and sparkling in all the colors of the rainbow. The superstition that it is unlucky for anyone born in any month other than October to wear an opal came from the novel “Anne of Geierstein” by Sir Walter Scott written in the 1800’s. Opal has actually been considered to be the luckiest and most magical of all gems because it can show all colors. It was even thought to have the power to preserve life and be color of blond hair. For ages, people have believed in the healing power of opal and it is reported to cure depression and help its wearer find the true and real love. They are believed to enhance the positive characteristic of people born under the zodiac sign of Cancer. Black opal is recommended for those born under Scorpio and Boulder Opal is a lucky stone for Aries. Opals became prevalent in jewelry during the Art Deco period.
It is thought that opal formed 15 to 30 million years ago with one exception in Australia where at Mintabie it is thought to have formed about 400 million years ago. It is formed in desert areas that have strong seasonal rainfall and rocks rich in silica. The water seeping through the rock carries silica that is evaporated out in pockets of rock. However opal still contains a significant amount of water usually about 3 to 10% and can be as high as 20%.
In 1849 the first opal blocks were accidentally found on the Australian cattle station of Tarravilla. Prospecting started in 1890 at White Cliff in Australia. Other famous opal areas of Australia are Lighting Ridge, Andamooka and Coober Peddy (aborigine word for “white man in hole”). The largest opal found is 6,843 kilogram known as the Andamooka Desert Flame.
Source
Australia produces black and white opal. Brazil produces white opal. Mexico produces Fire Opal. Peru produces Peruvian opal. Ethiopia and Malawi produces white opal.
Properties
- Hardness: 5.5 – 6.5
- Toughness – very poor to fair.
- Reaction to Heat – High heat or sudden temperature change can cause fracturing.
- Reaction to Light – Stable but heat from intense light can cause fracturing (known as crazing)
- Reaction to Chemicals – Attacked by hydrofluoric acid and caustic alkalis
- Clarity – Fractures, pits, surface blemishes, matrix, crazing (a fine network of cracks that resembles spider’s web).
- Most popular cut is cabochon. The Mexican opal is often faceted as well.
- Confused with Ammolite, mother-of-pearl, labradorite, moonstone. Imitations include opal doublet or triplets and synthetic opal (Gilson) and simulated opal made of glass (Slocum) and a Japanese plastic opal.
- Treatments/Enhancements –
- Impregnation with oil, wax, or plastic – improves play-of-color and prevents or disguises fracturing. Black plastic creates appearance of black opal – stability is fair to poor for oil or wax and excellent for plastic.
- Sugar treatment – soaking in dye, silver nitrate or sugar and acid – creates or improves play-of-color and simulates appearance of black opal. – stability is poor to good
- Smoke impregnation – creates or improves play-of-color and simulates appearance of black opal – stability is fair to poor because treatment is shallow and abrades or chips away easily.
Loss of moisture and crazing can result from storage in airtight containers such as safe deposit boxes
Fire Opal Earrings
Types of Opals
- White Opal – translucent to semi-translucent with play-of-color against a white or gray bodycolor.
- Black Opal – translucent to opaque with play-of-color against a black or other dark bodycolor
- Fire Opal – transparent to translucent with brown, yellow, orange or red bodycolor. This material often doesn’t have play-of-color is also known as “Mexican opal”, “Gold opal”, or “Sun opal”.
- Boulder Opal – Opal with dark base surface with play-of-color and occurs as pebble rock where the opal fills hollows.
- Harlequin Opal – transparent to translucent opal with effective segment like color patterns.
- Jelly Opal (Water Opal) – bluish-gray opal with little play-of-color.
- Crystal Opal – a few red reflexes on colorless, vitreous surface.
- Girasol – almost colorless, transparent opal with bluish luster
- Peruvian Opal – a blue-green mostly opaque with very little play of color opal found in Peru.
- Assembled Opal – precious opal layers and other material cemented together to improve durability and appearance.
Custom Boulder Opal Pendant
Play-of-Color
Play-of-color is caused by sub-microscopic spheres stacked in a grid-like pattern (like layers of ping-pong balls). This structure breaks up light into spectral colors. The colors depend on the size of the spheres. 0.1 micron in diameter produces violet. 0.2 micron in size produces red. In between sizes produce intermediate hues.
- Pinfire or pinpoint – small, close-set patches of color.
- Harlequin or mosaic – broad, angular, close-set patches of color.
- Flame – sweeping reddish bands or streaks that shoot across the stone
- Peacock – mainly blue and green
Care
- Cleaning methods
- Ultrasonic – Never
- Steamer – Never
- Warm soapy water – safe
Birthstone for October
14th wedding anniversary stone
