Picture Jasper is a name for jaspers which show a picture once cut into a slab or cabochon.
The pictures form through weathering events which create patterns on the outside edge of the rock. When cutting the pictures tend to stick to the outside of the stone. The longer and more the jasper has weathered, the more interesting the patterns get.
Sometimes metal dendrites grow on the weathering rings which can only happens if the material is in a gel state. These stones are not just beautiful but fascinating!
Most picture jaspers start their life as a silica rich mud which eventually uptakes so much silica it becomes a quartz family mineral.