A classic specimen of Fluorite from the famous Cave-in-Rock area of Illinois, USA. The Fluorite shows sharp cubic form with crystals to 4.6cm on edge. The crystals have a silky luster. The body colour of the crystals is a translucent light yellow, overprinted by a colour zone of light purple, in turn covered by a colourless zone, with finally a very thin rind of light purple - the last to be precipitated. The colourless zone seems to be the host area for sharp metallic crystals of Chalcopyrite. Specimens from this area display very nicely when backlit.