Demo specimen photos via Wikimedia Commons — final Smithsonian GeoGallery specimens to follow.
A banded variety of chalcedony quartz, agate forms in concentric layers that create its signature stripes, swirls, and eye-like patterns. No two pieces are alike: it ranges from soft translucence to bold graphic banding in nearly every color nature offers. Cut, polished, and cabochon-finished, it is one of the most artistically versatile stones in jewelry.
