Agates mostly occur as nodules in volcanic rocks or waters containing silica in solution possibly derived from the decomposition of silicates in the lava. The siliceous matter is deposited in regular layers resulting in the banded or striped formation. Many times this beautiful material is made into bookends, spheres, eggs, and many other collectible items.Agate Formation and characteristics Named after a river in Sicily , called Achates-Agate is the most common form of chalcedony, and is a versatile commericial stone. Agate with a cavity is called a geode. Hardness is a 6.5.
Most agates occur as nodules in volcanic rocks or ancient lavas where they represent cavities originally produced by the disengagement of volatiles in the molten mass which were then filled, wholly or partially, by siliceous matter deposited in regular layers... read more