Pyrite after Brachiopod

Unknown Owner

A wonderful example of crystallized pyrite replacing a previous brachiopod fossil. In great condition all around.Pyrite pseudomorphs after fossil brachiopods represent a fascinating intersection of paleontology and mineralogy, where a biological structure is replaced by a mineral while retaining its original shape. Geologically, this process typically occurs in anaerobic, iron-rich marine sediments where sulfate-reducing bacteria facilitate the precipitation of pyrite (iron disulfide) within the shell cavities or by replacing the original calcitic shell material entirely. This chemical replacement, known as pyritization, is common in organic-rich shales and limestones, such as the Devonian-aged deposits of the Hamilton Group in New York or similar formations in Ohio. Historically, these unusual specimens have been documented and collected since the 19th century, often found as a byproduct of limestone quarrying or during specialized paleontological excavations.