Banded Agate

Agate is a banded variety of chalcedony, a form of silica (SiO₂) made of quartz crystals too small to see. In banded agate the layers form stripes or rings, in shades of white, cream, orange and brown.

Agate forms in cavities inside rock. Silica-rich water seeps into the cavity and deposits layer after layer, along the walls or from the floor up. Changes in the water's makeup over time create the bands, and various impurities give them their colors.

Even so, exactly what happens in there is still largely a mystery: no one has ever managed to reproduce agate banding in a lab. Some things only nature can do, with the patience of millions of years.

The name comes from the Achates River in Sicily, where agates were found in ancient times. The Greek philosopher Theophrastus wrote about them around 350 BCE, although the river was probably named after the stone rather than the other way around. The Sumerians, Egyptians and Romans used agate for jewelry and decorative objects.

Agate is slightly porous, which makes it easy to dye. Most of the brightly colored agates on the market have been dyed, a practice that developed in 19th-century Germany. Agate in natural colors has a more understated look.