The vast majority of stone being sold as "onyx" is not onyx at all.
Onyx is a black and white banded variety of agate. Onyx and agate are both types of chalcedony.
The confusion over the precise definition comes from geological variations, overlapping terminology, subjective classification and evolving scientific understanding of this mineral.
The stones that we currently have in our collection are calcite.
They are however sold as "onyx".