Onyx, Traditionally onyx is a term reserved for a particular type of black agate material usually with bands of white running through it. Today the term is more general, and can refer to a material that is semi-translucent regardless of it coloration, vein type, hardness, or specific mineral composition. Because of the broadening definition (considered to be inaccurate in a geological sense) of this material category, onyx materials can vary in hardness and susceptibility to acidic environments. In large, the industry recognizes onyx as a rock materials with a natural translucency. Due to this distinction it is often set on metal frameworks and backlit to achieve a dramatic look for ceiling lighting fixtures, shower walls.