1. Min. Chalcedony in parallel layers of different shades of color. It is used for making cameos, the figure being cut in one layer with the next as a ground.
Onyx marble, Mexican onyx, a banded variety of marble or calcium carbonate resembling onyx. It is obtained from Mexico in various colors ranging from white to deep black.
n : a chalcedony with alternating black and white bands; used in
a hail; claw; hoof, (Heb. shoham), a precious stone adorning the
breast-plate of the high priest and the shoulders of the ephod
(Ex. 28:9-12, 20; 35:27; Job 28:16; Ezek. 28:13). It was found
in the land of Havilah (Gen. 2:12). The LXX. translates the
Hebrew word by smaragdos, an emerald. Some think that the
sardonyx is meant. But the onyx differs from the sardonyx in
this, that while the latter has two layers (black and white) the
former has three (black, white, and red).