(σαρδόνυξ)
The sardonyx is the fifth foundation of the New Jerusalem (Revelation 21:20). This stone is a beautiful variety of onyx, consisting, as the name implies, of a layer of sard (or of carnelian) with one of white chalcedony, or presenting several alternating layers of these minerals. The finest kind known to ancient writers-now called the ‘Oriental sardonyx’-had at least three strata-a black base, an intermediate band of white chalcedony, and a superficial layer of red or brown. The black was regarded as typifying humility, the white chastity, and the red modesty or martyrdom. The sardonyx was frequently used for seals and cameos. The best kind was obtained from India or Arabia. Imitations are made by cementing together stones of the required colours, or by placing a sard or carnelian, coated with sodium carbonate, on a red-hot iron and so producing a white layer.
James Strahan.