Smith's Bible Dictionary
Onyx. (a nail). Onyx is the translation of the Hebrew shoham; but there is some doubt as to its signification. Some writers believe that the "beryl" is intended; but the balance of authority, is in favor of some variety of the onyx.
("The onyx is not a transparent stone, but as the color of the flesh appears through the nail, (Greek, onyx), on the human body, so the reddish mass which is below, shines delicately through the whitish surface of the onyx. There are several varieties. White and reddish stripes alternating form the sardonyx; white and reddish gray, the chalcedony. When polished, it has a fine lustre, and is easily wrought into a gem of great beauty." - Rosenmiller.
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Smith, William, Dr. Entry for 'Onyx'. Smith's Bible Dictionary. https://www.studylight.org/dictionaries/eng/sbd/o/onyx.html. 1901.