Agate is a rock consisting primarily of cryptocrystalline silica, chiefly chalcedony, alternating with microgranular quartz. It is characterized by its fineness of grain and variety of color. Although agates may be found in various kinds of host rock, they are classically associated with volcanic rocks and can be common in certain metamorphic rocks.
This beautiful large polished agate slices comes from southern Brazil. The stone has been soaked in a dye solution which allows the natural agate to absorb the colorations. The agates formed within air pockets of hardened lava. Silica rich fluids flowed through these air pockets and began to cool and harden. Layer upon layer of silica built up within the pocket, creating beautiful bands. The front and back has been cut and polished to a high gloss finish, while the edges of the stone have been left in its raw state.