Amethyst

one of the precious stones in the breastplate of the high priest (Ex. 28:19; 39:12), and in the foundation of the New Jerusalem (Rev. 21:20). The ancients thought that this stone had the power of dispelling drunkenness in all who wore or touched it, and hence its Greek name formed from a_, "privative," and _methuo , "to get drunk." Its Jewish name, ahlamah' , was derived by the rabbins from the Hebrew word halam , "to dream," from its supposed power of causing the wearer to dream. It is a pale-blue crystallized quartz, varying to a dark purple blue. It is found in Persia and India, also in different parts of Europe.

Source: Easton’s Bible Dictionary (M.G. Easton, 1897, public domain).