Tuscumbia chert

Tuscumbia chert comes from the Paleozoic Tuscumbia Formation, which overlies the Fort Payne Formation in Tishomingo County, Mississippi. Usable stone is black to blue-gray or brown, glassy, and opaque to slightly translucent. It usually forms nodules with a chalky, crumbly outer rind and a zone of light brown chert just inside, sometimes with feathery banding that looks like woodgrain. When streams roll the nodules, the chalk wears off and leaves a smooth milk-chocolate brown skin. The blue-gray variety can be mistaken for Bangor chert, and because silica moved freely between the two limestones, similar chert exists in both.

Paleozoic Tuscumbia Formation (mapped on the 1969 state map with Fort Payne as limestones, cherts and shale of Meramec, Osage and Kinderhook age), the younger of the two chert-bearing limestones in Tishomingo County, northeast Mississippi; the older Fort Payne Formation lies beneath it with chert beds at the contact. Mississippi's survey stresses that diagenetic silicification does not stop at formation boundaries, so similar chert can occur in either. Tuscumbia chert is abundant in stream alluvium of drainages cutting the formation, and it contributed to the chert gravels of the Cretaceous Tuscaloosa Formation.