Fern Fossil

A fabulous fossilized fern plate from the Llewellyn Formation, in St. Clair, Schuylkill County, Pennsylvania. These fossils date back approximately 300 million years to the Pennsylvanian Period, a geologic time filled with plant growth.

When plants such as the ferns seen here are consumed by swamps, the low oxygen environment allowed the plant matter to slowly be replaced by pyrite. It is believed that pyrophyllite, an aluminum silicate mineral, replaced the pyrite at a later stage, creating the white color you see today. 

The fern and plant impressions left behind create a beautiful contrast against the dark gray shale rock matrix. On the reverse side additional ferns can be seen in both white and orange iron-oxide colors.