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Fern fossil, from Mason Creek, Illinois


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Age & Formation: 
Pennsylvanian, ~310 Ma.
Geohistory: 
Classic specimen from the famous Mason Creek (Illinois) locality. The fern fossils are found within concretions. Apparently, ground water containing dissolved iron moved through buried Pennsylvanian strata, and the local presence of organic material caused progressive precipitation of iron oxides. Concretions built up as a result. Tapping the concretion with a hammer can cause the concretion to split right along the leaf. Delicacy of preservation is amazing. With a magnifying glass it is possible to see spores preserved on these leaves.
Whereabouts: 
Mason Creek locality to be sure, …but this specimen coming to me resulted from casual conversation with a fellow passenger on a flight back east in the mid-1980s. We got talking about geology, and it turns out he was a rock hound and had collection of Mason Creek specimens. He sent me this fossil a few weeks later! I love it. Who wouldn’t?