Agate rocks are formed when the silica in groundwater settles in cavities in igneous volcanic rocks. These solutions are formed by the crystallization of silicate phases in the cooling magma and the accumulation of silica in the lava rock cavity. The larger the host cavities, the greater the chance of producing this gem in larger sizes.
These sediments sometimes form a thin sequence of dense, circular silica layers around the cavity walls, sometimes forming flat layers from the bottom of the cavity upwards. These layered structures are one of the features of this gemstone, which can be seen in different colors with the presence of impurities in the solution.