Replacement takes place when water dissolves the original hard parts and replaces them with mineral matter. This chemical action may take place slowly, reproducing the microscopic structures of the original organism. Bone, shells and wood are often well preserved in this manner.
Minerals can replace bone, shell, wood, and even soft body parts as they dissolve away due to the action of water and decay. Replacement and mineralization are terms used to describe this fossilization process. During replacement coats of bacteria quickly mineralize the decaying tissue. If replacement results in a fossil that is completely articulated with three-dimensional fidelity the process is referred to as mineral replication. Organic residue on compression fossils can be replaced by minerals leaving an impression coated with a mineral.
|Gastropod Shell Formed by Mineral Replacement
Photo Credit: Frank Wesselingh