Onyx

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).