AMETHYST
(Heb. “achlamah”).
Precious stone in the third row of the high priest’s breastplate (Ex. 28:19; 39:12), and twelfth foundation of the heavenly Jerusalem (Rev. 21:20).
This gem has not been identified in a specific way. It could be the purple variety of corundum, known as oriental amethyst, or the transparent amethyst quartz that contains manganese and alumina.