Discovered by Stuart Hughes in Australia, this stunning $1-million opal just might be the largest in the world, at 55,000-carats. It measures 30cm in length, 15-20cm tall, and it’s around 4cm thick. Opals are basically a hydrated amorphous form of silica; its water content may range from 3% to 21% by weight, but is usually between 6% to 10%. Continue reading for one more picture and additional information.

The internal structure of precious opal makes it diffract light; depending on the conditions in which it formed it can take on many colors. Precious opal ranges from clear through white, gray, red, orange, yellow, green, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the reds against black are the most rare, whereas white and greens are the most common. It varies in optical density from opaque to semi-transparent. For gemstone use, its natural color is often enhanced by placing thin layers of opal on a darker underlying stone, like basalt. Common opal, called “potch” by miners, does not show the display of color exhibited in precious opal.

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