An ornamental stone that is a variety of agate, a kind of chalcedony. It is an onyx composed of two or more layers of milk-white chalcedony and transparent red sard. However, the contrasting layer is sometimes golden or brown. The red layer showing through the white one appeared much like the color of a fingernail to the Greeks, which was probably why they applied to it the Greek word oʹnyx (meaning “fingernail”), from which the English term “onyx” is derived. Sardonyx is found in various places, including Palestine and Arabia.
Sardonyx was valued in ancient times for engraved jewels, cameos, intaglios, and seal rings. The stone is mentioned once in the Bible, at Revelation 21:2, 19, 20, where the fifth foundation stone of “the holy city, New Jerusalem,” is a sardonyx stone.