Agates form as nodules within the cavities of volcanic rocks. These cavities are formed from the gases trapped within the liquid volcanic material forming vesicles. Cavities are then filled in with silica-rich fluids from the volcanic material, layers are deposited on the walls of the cavity slowly working their way inwards. The layers are made of quartz and chalcedony and the different colours are the result of different compositions of the fluids in the cavities.
This agate is from Scurr Hill, Fife, Scotland and has been hand polished to reveal the stunning colours.