This is one beautiful and shiny fossil! It appears to be a Strobeus pyrite gastropod fossil. It was found in a coal mine at a depth of 60-250 meters. More pictures below show some more specimens that were found.
My identification source is Fossils of Ohio (Bulletin 70, Rodney M. Feldmann Editor, State of Ohio, Department of Natural Resources, Division of Geological Survey, Columbus Ohio 1986) pages 162-173, figure 24 of specimen from Putnam Hill shale (Allegheny Group, Pennsylvanian) Vinton County Ohio, OSU 46701.
The fossil was situated above the coal seam so it might be from the Pennsylvanian Period (late Carboniferous). It was found in Webster County Kentucky USA. The mines there are part of the Eastern Interior Basin. The formations found there are Sturgis, Carbondale, and Tradewater. The limestone layers are Carthage, Madisonville, Providence, Yeargiss?, and Lead Creek.
Learn more about the geology of this area at the United States Geological Survey:
http://pubs.usgs.gov/pp/p1151h/penn.html
