This set of 3 agate slabs includes one of each color: brown, black, and blue. These rocks were naturally formed, cut into slices, and then polished to make beautiful agate specimens. Since these agates were naturally formed by the earth, specimens will vary in structure and will be unique. All agates are made of cryptocrystalline silica, primarily chalcedony, alternating with microgranular quartz, with some crystal structures being visible to the naked eye. Each slab measures at least 3.5 inches in length, but may be longer. Thickness measures approximately 5mm.