This remarkable form of pyrite is found in narrow seams of shale between seams of coal in the mines near Sparta, Illinois near the 300 foot level. Scientists are not sure of their origin. The main theory is that they are an undetermined fossil that has been replaced by pyrite. At any rate, they are quite remarkable, a shimmering golden color, and complete all around, like a sand dollar.
Attribution: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0
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