(Science: chemical) Chalcedony in parallel layers of different shades of colour. It is used for making cameos, the figure being cut in one layer with the next as a ground. Onyx marble, a banded variety of marble or calcium carbonate resembling onyx. It is obtained from Mexico.
Origin: L, fr. Gr. A claw, finger nail, a veined gem. See Nail, and cf. Onycha.