Agate is a variegated class of Chalcedony, usually displaying different color bands or other patterns- though some Agate is not patterned and displays opaque translucency. Agate was first discovered by Pliny in 77 A.D. and was named for the River Achates in Sicily.
Chemical composition: SiO₂ with other polymorphs of silica; Hardness: 7
The term geode refers to a spherical mass of mineral material with a hollow cavity in the center. Though sometimes filled, the center cavity usually contains some crystalline material, most often quartz.
The drusy center of this geode is composed of a mass of tiny quartz crystals that sparkle like diamonds.