Chalcedony ( , or  ) is a  form of , composed of very fine intergrowths of  and . These are both silica , but they differ in that quartz has a  crystal structure, while moganite is . Chalcedony's standard  (based on the chemical structure of quartz) is SiO₂ ().

Chalcedony has a waxy luster, and may be semitransparent or translucent. It can assume a wide range of colors, but those most commonly seen are white to gray, grayish-blue or a shade of brown ranging from pale to nearly black. The color of chalcedony sold commercially is often enhanced by dyeing or heating.

^{Sterling Silver Setting}

^{1 1/4" long}

^{1/4" wide}