Onyx is a banded variety of the oxide mineral chalcedony. Agate and onyx are both varieties of layered chalcedony that differ only in the form of the bands: agate has curved bands and onyx has parallel bands. The colours of its bands range from white to almost every colour (save some shades, such as purple or blue). Commonly, specimens of onyx contain bands of black and/or white. It is very sophisticated material can be used in many forms.