The Greek Philosopher Theophrastus was the one who found Agate on the Shore of the Dirillo River in Sicily around the 3rd and 4th BC. Agate minerals have the tendency to form on or within Pre-Existing Rocks, creating difficulties in accurately determining their time of formation. 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. Agate is very durable and therefore is often seen detached from its eroding matrix. Agates have also been found in sedimentary rocks, normally in limestone or dolomite, these sedimentary rocks require cavities often from decomposed branches or other buried organic material. Silica-rich fluids are able to penetrate into these cavities and agates are formed.
Variations in the character of the solution or in the conditions of deposition may cause a corresponding variation in the successive layers. These variations in layers result in bands of chalcedony, often alternate with layers of crystalline quartz. Most commonly known Agate Stones are: (1) Lace Agate, (2) Moss Agate, (3) Turritella Agate, (4) Coldwater Agates, (5) Greek Agate, (6) Brazilian Agate and (7) Polyhedroid Agate.