Amethyst

Amethyst (Hebrew 'ahlamah; Greek amethystos) is a purple variety of quartz prized as a gemstone in the ancient world. It was set in the third row of the high priest's breastplate, the twelfth stone in the four-by-three arrangement of twelve gems representing the twelve tribes of Israel (Exod. 28:19; 39:12). In Revelation 21:20 amethyst is listed as the twelfth stone in the foundations of the walls of the New Jerusalem, maintaining a symbolic correspondence with the breastplate's arrangement. Ancient Egyptians and Greeks used amethyst extensively for seals and amulets; the Greek name derives from a belief that the stone prevented intoxication.