Agate

Agate is a type of chalcedony quartz that forms in concentric layers of a wide variety of colors and textures. They may be found in various kinds of rock, but are generally associated with volcanic rocks; each individual agate forms by filling a cavity in the host rock. Agate was given its name by the Greek philosopher Theophrastus who discovered the stone along the shore of the river Achates. In ancient times, agate was highly valued as a talisman of amulet said to quench thirst and protect against fever.