The name Onyx comes from the Greek word meaning fingernail. Black isn’t the color normally associated with fingernails but in Greek times almost all colors of chalcedony from white to black and even brown were called onyx. Later the Romans narrowed the term Onyx to refer to black & dark brown colors only.
Onyx is a banded variety of the mineral chalcedony. It differs from Agate which is also a layered chalcedony by the forms of the bands. Onyx has parallel bands while Agate has curved bands.
The history of use for Onyx has been for stone carvings and jewelry where it is usually cut into cabochon or into beads. It has also has been used for intaglio cameo engraved where the bands make the images contrast with the ground.
Onyx can also be used in counter tops. While granite and marble are forged deep within the earth’s crust, Onyx is formed right on the surface.
Most Black Onyx is color enhanced to increase its depth of color but does not decrease its value. Green Onyx has become very popular in lieu of jade.
Onyx is mined in Brazil, India, California and Uruguay.