Scientific Name: Banded chalcedony
Group: Silicates - tectosilicates
Chemical composition: SiO2
Colors: Light to dark brown banding.
Formation: Hexagonal/trigonal crystal; Cryptocrystalline form
Principal Sources: Sri Lanka; India; Brazil; Uruguay.
Special Notes: Sardonyx is a banded variety of chalcedony. The colors of its bands range from white to almost every color (save some shades, such as purple or blue). Commonly, specimens contain bands of colors of white, tan, and brown. It has been used since ancient times for the making of cameos.