Slice of Agate "almost a planet" from Brazil.

Agates are part of the silicate minerals, and their origin start deep inside the earth: basaltic lava flows, full of gaz, heading toward the surface are sometimes solidified on their way. The gaz pockets that remain trapped will be filled by each hydrothermal fluid circulation. Each oxyd or mineral contained in such fluids -mainly silicate gel- will add some colors to the previous deposit: hematite, limonite, manganese or green chlorite... Cut into thin slices, it becomes translucent and lets light through. This is quite remarkable in photo 3: it will do this effect every time it is in front of a window or other light source... Its composition is rare because it "filled" around nucleus, and water loaded with iron oxides deposited a layer with each big change of temperature, by evaporation. Almost the surface of a planet...