<p>Pyrite snake concretion from the Devonian of Ohio, USA (field of view ~4.6 centimeters across).
</p><p>This remarkable mass of coarsely-crystalline pyrite (fool's gold) is likely a pyritized burrow (trace fossil).  It comes from an Upper Devonian black shale succession - the Ohio Shale.  Pyrite is common in the Ohio Shale, occurring as small, disseminated specks and framboids to moderately large, coarsely-crystalline concretions.
</p><p>Stratigraphy: Ohio Shale, Famennian Stage, upper Upper Devonian
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Locality: creek cut in Ross County, southern Ohio, USA
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/47445767@N05">James St. John</a>
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<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/jsjgeology/15403897737/">Pyrite snake concretion (Ohio Shale, Upper Devonian; creek cut in Ross County, southern Ohio, USA) 7</a>