3.7" Fossil Seed Fern (Alethopteris) Plate Pos/Neg - Pennsylvania

This is a pair of 3.7" wide fossil seed ferns plates from the Pennsylvanian aged (305 million year) Llewellyn formation of Pennsylvania. Because of the way this material splits, both sides of the split rarely turn out like this. The white color of these detailed fern fossils contrasts well against the black shale they are preserved in. There are fossils covering both sides of the piece. These St. Clair fern plates used to be quite common but access to the locality is now restricted so there is not a lot of material left on the market.

Each half includes a display stand.

These plants were buried in a swamp where a low temperature, low pressure, and low oxygen environment caused the plant tissue to be slowly replaced by pyrite. This pyrite was later replaced by a whitish mineral (aluminum silicate) as the fossils were buried and exposed to the heat and pressure inside of the earth. The majority of the ferns on this plate are of the genus Alethopteris, though Pecopteris ferns can be seen from time to time.