Onyx is a banded variety of the mineral chalcedony. Agate and Onyx are both members of the same family, however Agate grows in curved bands, while Onyx grows in parallel ones. Onyx sits at a 6.5-7 on the Mohs Scale of Hardness.
Onyx is thought to be a strength giving stone that gives support when dealing with extreme physical or emotional stress. It is also associated with vigor, stamina, strength, confidence and self control.