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Smithsonian National Museum of Natural History


Photograph of opal (NMNH G9266) from the National Gem Collection
Photo by Chip Clark. Click to zoom.
Catalog Number NMNH G9266-00
Locality South Australia, Australia
Weight 174.86 ct

From the exhibit

World-famous Australian opal (below) formed when silica-rich groundwater trickled down through sediments until stopped by a layer of clay. As water evaporated from the trapped solution, the silica formed microscopic spheres that settled into an orderly arrangement.


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