SARDONYX, a name applied to those varieties of onyx, or stratified chalcedony, which exhibit white layers alternating with others of red or brown colour. The brown chalcedony is known to modern mineralogists as sard and the red as camelian. The simplest and commonest type of sardonyx contains two strata,—a thin layer of white chalcedony resting upon a ground of either carnelian or sard; but the sardonyx of ancient writers generally presented three layers—a superficial stratum of red, an intermediate band of white, and a base of dark brown chalcedony. The sardonyx has always been a favourite stone with the cameo-engraver, and the finest works have usually been executed on stones of five strata. Such, for instance, is the famous Carpegna cameo, in the Vatican, representing the triumph of Bacchus and Ceres, and reputed to be the largest work of its kind ever executed (16 inches by 12). When the component layers of a sardonyx are of fine colour and sharply defined, the stone is known in trade as an “Oriental sardonyx”—a term which is used without reference to the geographical source whence the stone is obtained. A famous ancient locality for sard was in Babylonia, and the name of the stone appears to be connected with the Persian word sered, “yellowish red,” in allusion to the colour of the sard. Pliny, relying on a superficial resemblance, derives the name from Sardis, reputed to be its original locality. The sardonyx is frequently stained, or at least its colour heightened, by chemical processes. Imitations are fabricated by cementing two or three layers of chalcedony together, and so building up a sardonyx; while baser counterfeits are formed simply of paste. See Onyx, vol. xvii. p. 776.

σαρδόνυξ, Rev. xxi, 20. A precious stone which seems to have its name from its resemblance partly to the sardius and partly to the onyx. It is generally tinged with black and blood colour, which are distinguished from each other by circles or rows, so distinct that they appear to be the effect of art.