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Opal is October's first birthstone
02 February 2018
If you’re lucky enough to be an October baby, you have two birthstones to choose from – opal and tourmaline. Both are equally gorgeous but they’re radically different to each other and require different levels of care.
Let's start with opal....
Perhaps one of the most beautiful gemstones around, opal is a hydrous silicate mineral that typically contains 6 – 10% water content. Opal is an amorphous mineraloid that forms via the deposition of mineral salts in the fissures of rocks. Australia is the world’s leading supply of opal, accounting for approximately 95% of the world’s opals, but opal is also mined in Mexico, Brazil, Honduras, Ethiopia, the Czech Republic and parts of the U.S.A.
The name “opal” originates from the Greek word opallios, which meant “to see a change in color.” The Roman scholar Pliny used the word opalus when he wrote about this gem’s kaleidoscopic “play” of colors that could simulate shades of any stone.
Best known for its flashing rainbow colors called play-of-color, there are two broad classes of opal: precious and common. Precious opal displays play-of-color, common opal does not. Opal hues can range across the spectrum; an opal might display a single color, two or three colors, or all the colors of the rainbow.
Opal’s characteristic “play-of-color” was explained in the 1960s, when scientists discovered that it’s composed of microscopic silica spheres that diffract light to display various colors of the rainbow.
Because of opal’s high water content, it is a relatively soft gemstone, with a hardness of 5.5 to 6 on Moh’s hardness scale. As such, it is best suited for setting in earrings, pendants and brooches, where the jewellery is unlikely to encounter knocks and impacts. When used in a ring, the best designs have a bezel that protects the stone - instead of being placed in a prong setting that allows the edges of the stone to be exposed.
The world’s largest and most valuable opal, “Olympic Australis,” came from Coober Pedy, Australia in 1956, during the Olympic Games in Melbourne. Valued at $2.5 million in 2005, this gem measures 28cm long and weighs 17,000 carats (3.45kg).
If you’re looking for loose opals for setting in bespoke jewellery, give us a call at Katannuta Diamonds and let us help you select your perfect opal.