Sardonyx << SAHR duh nihks or sahr DON ihks >> is a variety of chalcedony, a fine-grained form of the mineral quartz. Most sardonyx has straight or slightly curved bands of reddish-brown and white. The chief sources of sardonyx are Brazil, Uruguay, and India. Sardonyx is one of the less expensive gemstones. It is used in jewelry. Jewelers usually cut it flat or with a domed shape to bring out the bands of color. Cameos are sometimes cut from sardonyx to take advantage of its color. Sardonyx is one of the birthstones for August.
See also Cameo; Chalcedony; Onyx.
