10.9" Fossil Seed Fern (Alethopteris) Plate - Pennsylvania

This is a 10.9" wide plate of fossil seed ferns from the Pennsylvanian aged (306 million year) Llewellyn formation of Pennsylvania. 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 allowing for two display options. 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.

It includes a display stand.

These plants were buried in a swamp where a low temperature, pressure, and oxygen environment the plant tissue was 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. There are multiple types of seed ferns (which look very similar) on these plates including Alethopteris and Pecopteris.