Bochum - Deutsches Bergbau-Museum - Steinkern 02
This photo shows a internal mould, by the end of a living being or living being part , on this occasion, running by sedimentation processes so slowly that the living being rots or hard parts resolve and a hollow cavity in the surrounding rock leaves which is filled with the time by trickling silicon, internal mould originate as fossils. With this process the original shape of the interior of an animal is preserved.
The fossil shown here, maybe a Sigillaria or Lepidodendron, was found in 1938 in a Osnabrück pit "Piesberg" and is approx. 300 million years old.