Onyx is the most traditional black gemstone, and it is the name used to commonly refer to solid black Chalcedony, or a banded or layered black and white Chalcedony. Onyx combines translucent and opaque bands consisting of fine intergrowths of silica minerals quartz and morganite. Its bands are parallel to one another as opposed to the more chaotic banding that often occurs in agates.
This property has, historically, made onyx a popular stone to use for engraving techniques as well as producing cameos, where a raised relief is produced to form a design that is lighter than the layer it sits on.
The ancient Romans entered battle carrying amulets of onyx engraved with Mars, the god of war. This was believed to bestow courage in battle.
Onyx is also associated to the Star sign Leo.
Onyx is a gemstone found in various regions of the world including Yemen, Uruguay, Argentina, Australia, Brazil, Canada, China, Czech Republic, Germany, India, Indonesia, Madagascar, Latin America, the UK, and various states in the US