Agate

Agate minerals have the tendency to form on or within pre-existing rocks, creating difficulties in accurately determining their time of formation.Their host rocks have been dated to have formed as early as the Archean Eon. Agates are most commonly found as nodules within the cavities of volcanic rocks. These cavities are formed from the gases trapped within the liquid volcanic material forming vesicles.Cavities are then filled in with silica-rich fluids from the volcanic material, layers are deposited on the walls of the cavity slowly working their way inwards