Kitto's Popular Cyclopedia of Biblial Literature
O´nyx. The Hebrew word translated by 'onyx-stone' in , is different from that so rendered in the descriptions of the breastplate of the high-priest (; ), and it is doubtful if the onyx is really intended by either. This stone has a whitish ground, and is variegated with bands of white and brown which run parallel to each other. It is a semi-pellucid stone of a fine flinty texture, taking an excellent polish, and is strictly of the flint or siliceous class. 'Onyx' is the Greek word for the human nail; and the stone takes its name from the resemblance of the ground-color to that lunate spot at the base of the nail.
Kitto, John, ed. Entry for 'Onyx'. "Kitto's Popular Cyclopedia of Biblial Literature". https://www.studylight.org/encyclopedias/eng/kbe/o/onyx.html.