This is one of the precious stones in the breastplate of the high priest (Exodus 28:19; 39:12), and in the foundation of the New Jerusalem (Rev. 21:20). It is mentioned only these three times in the Bible. It is probably the same gem that we are familiar with called the amethyst.
Some 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, the dream-stone, “achlamah” or “ahlamah”, was derived by the rabbis from the Hebrew word halam, “to dream,” from its supposed power of causing the wearer to dream.
The amethyst is a crystallized quartz, varying from purple, lilac, violet or mauve, to clear. In biblical times it was found in Persia and India, and also in different parts of Europe. Today, it is found in Brazil, Uruguay, Sri Landka, Siberia, Canada, India, Madagascar, Namibia, Russia and the USA.