It's only about as long as your thumb but it's worth more than $1 million. The finest opal ever discovered will be publicly displayed for the first time in September at the South Australian Museum in Adelaide as part of an exhibition celebrating this year's centenary of opal mining in Australia.
The 72 carat black opal, named the Virgin Rainbow, was dug up in 2003 in the South Australia town of Coober Pedy. Known as the opal capital of the world, the region produces 90% of the world's opals.
The Virgin Rainbow Opal "...appears to be in constant motion as the light refracts through it," museum director Brian Oldman says. "Rainbow is the right way to describe it. Yellows, reds, blues, blacks sparkle through this wonderful gem and as the light moves around it, the colours constantly change and mutate. It's an amazing trick of nature, how that has happened - and it only took a hundred million years to achieve it."
Opal is the product of seasonal rains that drenched dry ground in regions such as Australia's semi-desert outback. The showers soaked deep into ancient underground rock, carrying dissolved silica (a compound of silicon and oxygen) downward. During dry periods, much of the water evaporated, leaving solid deposits of silica in the cracks and between the layers of underground sedimentary rock. The silica deposits formed opal.
Opal's flashing play of kaleidoscopic color is caused by diffraction of light by the silica spheres. The arrays of silica spheres form fantastic patterns and colors. Opal's can display all the colors of the rainbow.
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