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Image credit: Chip Clark
The Roebling Opal is an extraordinary 2,585-carat piece of opal rough and is also the largest unpolished black Opal.

It came out of the tunneled portion of the Rainbow Ridge Mine in 1917 from Virgin Valley, Nevada. The opal was deposited from silica-rich water in voids that remained after buried tree limbs had rotted away, in some cases resulting in opal casts of the original tree parts.

Although extremely beautiful, opal from this locality is not commonly used in jewelry because it tends to craize, or crack. Opals with a vivid play-of-color and a black or other dark body color are called black opals. The Roebling Opal is a black opal with flashes of blue and green play-of-color.

The Roebling Opal was donated by John A. Roebling in 1926 and now rests with the Smithsonian National Museum of Natural History.




Image credit: Chip Clark
Image credit: Chip Clark

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