Amethyst

"Amethyst Intaglio," a portrait of the Roman Emperor Caracalla, changed in the Byzantine period into a portrait of St. Peter with the addition of an inscription and a cross, ca. 212 CE, from the Cabinet des Médailles in the Bibliothèque nationale de France, by Clio20. Licensed under CC By-SA 3.0.

Article: Amethyst Symbolism

Credit: Clio20