Permineralization preserves porous materials such as bones,
plants and shells. The material is buried, then water percolates through
it. A solution, commonly containing a lot of either calcium carbonate or
silica, precipitates minerals in the spaces. The original wood or shell
like material is preserved.
Recrystallization forms fossils out of bones and other hard
parts that are made from minerals. In this process the minerals
recrystallize. They regrow to make new, often larger crystals of the
Replacement involves the complete removal of the original hard
parts. The original minerals dissolve in water. They are replaced by
precipitation of new minerals. The Petrified Forest in Arizona is an
excellent example of this type of preservation. The original organic
material (wood) has been replaced by silica.
Replacement of mollusk fossils
Permineralization of a stem