Onyx,

opaque to slightly translucent, two-tone black and white layered, fibrous variety of chalcedony. Due to the high demand, which can not be covered by the natural resources, a large part of the commercially available onyx is imitiated. Mostly agate and chalcedony are manipulated or black obsidian is sold as onyx. If the stone is crisscrossed by white color, you can be assumed from a real specimen. For an accurate determination, however, a mineralogical investigation is necessary.