We specialize in affordable/cheap natural St. Clair PA Fern Leaf Plant Fossils/Display Slabs. These carboniferous ferns died 300 million years ago! They fell into a bog where a low temperature, low pressure, oxygen depleted environment evolved the plant tissue into Pyrite. Pyrophyllite(Aluminum Silicate) replaced the Pyrite at an ensuing stage, creating the bold, white color. Dozens of plant species are found in these fossiliferous shales, so look closely. Common species include Alethopteris, Neuropteris, Pecopteris, and Sphenophyllum. Seed ferns went completely extinct around 73 million years ago, while the dinosaurs were still around! Also buy Devonian Fossils, Minerals, Crystals, Books, more.