Definition of Amethyst, the February birth stone: The word Amethyst is derived from the Greek word "amethystos" which means "remedy against drunkenness" which is reflected in the properties of this stone. A variety of crystallized quartz, of a purple or bluish violet color, of different shades. It is much used as a jeweler's stone. The Amethyst is a member of the Quartz (silicon dioxide) family. Crystal structure of the Amethyst, the February birthstone, is hexagonal.