Everything You Need to Know About Opals
Opal, the birthstone for October, is usually thought of as an Australian-origin black, white, or pale colored gem that exhibits a myriad of iridescent colors. What many
don’t realize is that opal is actually an incredibly diverse gem type that doesn’t always have this iridescent effect!
Mysterious opals contain the wonders of the skies – sparking rainbows, fireworks, and lightning – shifting and moving in their depths. Opal has been treasured throughout history around the world. Archaeologist Louis Leakey found six-thousand-year-old opal artifacts in a cave in Kenya!
The story of opal in Australia begins more than 100 million years ago when the deserts of central Australia were a great inland sea, with silica-laden sediment deposited around its shoreline. After the sea receded and disappeared to become the great Artesian basin, weathering 30 million years ago released a lot of the silica into a solution that filled cracks in the rocks, layers in clay, and even some fossils. Some of this silica became precious opal. Opal is one of the few gemstones that is sedimentary in origin. Opal still contains six to 10 percent water, a remnant of that ancient sea. Gold panners in Australia found the first few pieces of precious opal in 1863. Mines at White Cliffs began producing in 1890.
Black opal is found only in Australia in Lightning Ridge, the most famous opal deposit in the world since it was discovered in 1903, and in Mintabie, which also produces large quantities of light opal.
Caring For Opals
The hardness of opal ranges from 5.5 to 6.5 on the Mohs scale. It should be protected from heat and strong light, which can dry it out, causing cracks. Ultrasonic cleaners, metal polish, acids, and any strong solvents should be avoided. Exposed corners or points on pear or marquise shape opals may chip if hit while they are being worn. Opal is best to set in a protected mounting.
Colin Nash, Certified Gemologist Appraiser, Nash Jewellers