Agate is a striped chalcedony quartz that forms in layers and in a wide variety of colors and textures. An individual agate forms by filling a cavity in a "host" rock. As a result, agate often is found as a round nodule, with concentric bands. In ancient times it was said to quench thirst and guard against fever, and agate bowls were very popular in historical Europe.

Onyx is a chalcedony quartz with a fine texture and black color. Some onyx also displays white bands or ribbons against a black background. Onyx was popular with the ancient Greeks and Romans. The name comes from the Greek word "onux," which means fingernail. The myth is that Cupid cut the divine fingernails of Venus one day while she was sleeping. He discarded the clippings and the fates turned them to stone so that no part of Venus would ever be lost. In Greek times, almost all colors of chalcedony from fingernail white to dark brown and black were called onyx. Later, the Romans narrowed the term to refer to black and dark brown colors only.