Chalcedony << kal SEHD uh nee or KAL suh `doh` nee >> is a mineral that consists chiefly of tiny crystals of quartz with extremely small pores. Common chalcedony, sometimes called white agate, is semitransparent and clouded with circles and spots. It has a waxy luster. Other kinds of chalcedony are nearly transparent and may have many colors. They include agate, carnelian, onyx, and sard. The petrified forests of Arizona were formed in part by water depositing chalcedony in the decaying woody fibers of trees.
Chalcedony is used chiefly as a gemstone and for ornamental purposes. A type called bloodstone is a birthstone for March. It is green with red spots.
Chalcedony was named for the ancient town of Chalcedon in what is now Turkey, which is near deposits of the mineral. Other notable deposits of chalcedony occur in Iceland and Scotland, and in California and Colorado.
