Onyx is traditionally the term used to refer to a type of Agate, which exhibits the colours Black and White only. Sometimes this type of Agate/Onyx is also called Sardonyx. This crystal exhibits a trigonal structure and has a hardness of 7 on the Mohs hardness scale.
The properties of this type of Onyx can be seen in the section under Agate, these stones provide stability, support, grounding and balance.
These “types” of onyx have created a great confusion around the true nature of Onyx, which is traditionally black and white banded agates.