The Book of Agates and Other Quartz Gems

Agate is a cryptocrystalline variety of silica, chiefly chalcedony, characterized by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks and can be common in certain metamorphic rocks. Agate is one of the most common materials used in the art of hardstone carving, and has been recovered at a number of ancient sites, indicating its widespread use in the ancient world; for example, archaeological recovery at the Knossos site on Crete illustrates its role in Bronze Age Minoan culture. There are many different kinds of agate - Mexican, Turritella, Greek, Brazilian, Rainbow, Lace, Polyhedroid, Holley Blue and many more - which are used for different things from industrial to art to jewelry.