One of the earliest writers to associate with the apostles the symbolism of the gems given in Revelations is by Andreas, bishop of Caesurae. He gives a brief description of the stones, which is recounted in George F. Kunz's book The Curious Lore of Precious Stones (1913).
* The Chalcedony . . . represented St. Andrew. Chalcedony: Hebrew name of Bareketh. *
Chalcedony - Any type of quartz which has a cloudy, non-crystalline appearance, such as agate. Its common colors are blue-gray, white (cream), and red-brown. A translucent to transparent milky or grayish quartz with distinctive microscopic crystals arranged in slender fibers in parallel bands.
Agate - The name agate comes from the Sicilian river formerly called Achates. The Drillo river (modern name of the Achates) is still a major source of this form of chalcedony. Early civilizations, including the ancient Egyptians, used agate for seals and protective talismans. Some of these civilizations created eye beads by carving a hole through an agate disc to symbolize the lens of an eye.
Quartz - A very hard mineral composed of silica, SiO2, found worldwide in many different types of rocks, including sandstone and granite. Varieties of quartz include agate, chalcedony, chert, flint, opal, and rock crystal.
Quartz that is formed not of one single crystal but finely grained microcrystals is known as chalcedony. The variety of chalcedony is even greater than transparent quartz varieties because it includes cryptocrystalline quartz with patterns as well as a wide range of solid colors. Included in the chalcedony family are Agates, Jasper, Carnelian, and Chrysoprase.
Gem lore attributes to chalcedony the ability to increase intellect and creativity. It is said that blue chalcedony makes one more telepathic while giving mental clarity, that it is balancing and reduces all negativity.