The name Agate is derived from the Sicilian river Achates where agates were probably found in antiquity.

Agate is banded chalcedony, sometimes containing opal substance. The individual bands can be multi-colored, or more or less the same color.

Agates are found in nodules or geodes in siliceous volcanic rocks. The bands are formed by rhythmic crystallization, but scientific opinions vary on how. It is thought the agate bands crystallize gradually in the hollows formed by gas bubbles from siliceous solution. The various bands especially those close to the outer wall may vary in thickness, but normally their thickness remain constant throughout the nodule. The outer wall and outer most layer may form a white crust due to weathering. (Refer; Gemstones of the world By: Walter Schumann)