Fossil Type

Permineralized Fossils

Permineralized fossils form when mineral-rich groundwater infiltrates the pores and cellular spaces of buried organic material, depositing minerals like silica, calcite, or pyrite within the original structure. Unlike replacement, the original organic material may still be present alongside the minerals, creating an exceptionally detailed record that can preserve cellular-level anatomy.

Formation

How Permineralized Fossils Form

The organism is buried in sediment before significant decay. Mineral-rich groundwater percolates through the remains, depositing minerals in empty spaces — cell walls, pores, vascular channels — without necessarily dissolving the original material. Over millions of years, the combination of original material and deposited minerals creates an incredibly hard, detailed fossil. Petrified wood is the most famous example.

Field Guide