Amethyst is a variety of quartz that is best know for it's rich, violet-purple hue.The color can vary in intensity from a pale, almost pinkish (mauve) color to a dark purplish violet.Agate is named as the second stone in the third row of the High Priest’s breastplate.Agates are a form of chalcedony (a fine-grained variety of quartz) that are banded or lined in a variety of patterns of colored layers.
Beautifully carved and engraved amethyst goblets, vases, charms and miniatures have been found in excavations.
At that time, emeralds, though also beryl, were called by another name, smaragdos (this being the fourth stone in the New Jerusalem). The best known beryl are the emerald (grass green in color), and the aquamarine (blue-green).
Both of these stones were well known in Bible times, the aquamarine being the most common.
In Revelation -20, John names twelve stones that adorn the foundation of the New Jerusalem.
The difficulty has been in knowing the exact identity of the stones named.
Pliny the Elder (23-79 AD) who was a historian at the time the Book of Revelation was written, describes the beryl (berullos) of that day, “The lapidaries cut all beryls of a hexagonal form because the color..heightened by reflections resulting from the angles.