DescriptionFossiliferous flint (Upper Mercer Flint, Middle Pennsylvanian; Nellie West Outcrop, Coshocton County, Ohio, USA) 1 (31803128551).jpg
Fossiliferous flint (chert) from the Pennsylvanian of Ohio, USA. (9.5 cm across at its widest)
"Flint" is the official gemstone of Ohio. Flint is actually chert (the two terms are synonymous, despite what anyone else might say), a cryptocrystalline, quartzose sedimentary rock. High-quality, colorful, multicolored, and multipatterned flint is moderately common at some Ohio localities. A couple famous flint occurrences in east-central Ohio include the Vanport Flint at Flint Ridge and Nellie Blue Flint in Coshocton County.
The rock shown above is from the Upper Mercer Flint, a somewhat persistent horizon of chertified marine fossiliferous limestone in east-central and eastern Ohio called the Upper Mercer Limestone. The Upper Mercer is usually a black flint with whitish speckles (= often body fossils and fossil fragments). This sample has a fossil solitary rugose coral exposed in transverse cross-section.
The light-colored rind at top is non-chertified Upper Mercer - in other words, limestone.
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