Black onyx is a variety of chalcedony (cryptocrystalline quartz). Sample.

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Photo credit: © José María Barres Manuel / Alamy / Afripics
License: Royalty Free
Model Released: No

Keywords: agate, black, chalcedony, close-, cryptocrystalline, geology, horizontal, mineralogy, onice, onix, onyx, quartz, sample, sardonyx, semiprecious