Chalcedony

The traditional or ancient birthstone for August, sardonyx is red and white layered onyx, a variety of chalcedony, itself a variety of quartz. Gem with intaglio of Bellerophon and Pegasus, sardonyx and gold, early 1st century CE, Roman Empire, from the collection of the Walters Art Museum. Photo licensed under CC By-SA 3.0.

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