Onyx is a banded variety of the oxide mineral chalcedony. The colors of its bands range from white to almost every color (with the exception of some shades, such as purple or blue). Commonly, specimens of onyx contain bands of black and/or white.
Black coating uses either ruthenium or TIN cobalt black to give a piece of jewelry a light black or completely black appearance. It is very durable and resistant to scratches. Black plating gives the jewelry piece a sense of masculinity and high-tech.