The term agate refers only to the translucent type of chalcedony in which the
color is distributed in curved bands or layers.
Agate is formed when circulating
ground waters approaching saturation in silica content fill a cavity in a host
rock or dissolve pre existing material such as bone or shell. As a result,
agate is often found in the shape of a round nodule, with concentric bands
like the rings of a tree trunk.
The bands sometimes look like eyes, sometimes
like scallops, or even like a landscape with dendritic trees, the latter variety
being called « moss agate ».
The name agate comes to us through Latin from the Greek word for the river Achates, in Sicily, where this material
was first found in significant quantities.
Agate is one of the first materials
known to man. According to legends it makes the wearer agreeable and persuasive.
Agate was also said to cure insomnia and give to its owner pleasant dreams.
The Sumerians seem to have been the first to use agate for seals, signet rings,
beads and other articles of jewelry. A famous collection of two to four thousand
agate bowls, which was accumulated by Mithridates, king of Pontus, shows the
enthusiasm with which agate was regarded in the Antiquity.
Agate bowls were also popular in the Byzantine Empire and collecting them became common among
European royalty during the Renaissance. Today many museums in Europe have
spectacular examples on display.
The Persians, the Arabs and other Oriental people principally used agate for finger rings. Upon these, usually figure
a carved verse from the Koran, the owner's name, or some magical or symbolic
figure to protect the owner from a wide variety of calamities.