Chrome Chalcedony is a green variety of chalcedony, which is colored by chromium compounds. Well-known types of chalcedony are carnelian, agate, and onyx. Carnelian is a color named after the carnelian variety of the mineral chalcedony. The carnelian is a siliceous stone and a species of chalcedony. Imitation dzi are created from materials other than agate or chalcedony. Onyx is a banded variety of chalcedony (quartz). Onyx is formed of bands of chalcedony in alternating colors. Onyx primarily refers to the parallel banded variety of the silicate mineral chalcedony. Artificial onyx types have also been produced from common chalcedony and plain agates. "Calcedonio" is a marbled glass that looked like the semiprecious stone chalcedony. These agates are typically less colorful, with banded lines of grey and white chalcedony. Other source materials include chalcedony, quartzite, andesite, sandstone, chert, and shale. Not an official gemstone, it is a siliceous chalcedony. This petrification process generally results in a quartz chalcedony mineralization. Dyed chalcedony, jasper, and marble is less common, and much less convincing.