Onyx: A hail; claw; hoof, (Heb. shoham), a precious stone adorning the
breast-plate of the high priest and the shoulders of the ephod
(Exodus 28:9-12,20; 35:27; Job 28:16; Ezekiel 28:13) It was found in the land
(Genesis 2:11-12) 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).