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Outcrops of St. Genevieve chert occur from Alton, Illinois to Randolph county, Illinois and from Union to Hardin county, Illinois (Willman 1975). St. Genevieve chert is located in the St. Genevieve limestone of Mississippian age. St. Genevieve limestone overlies St. Louis limestone (Willman 1975). There are two subgroups of St. Genevieve chert, Rootbeer and Old Blue (DeMott 1993). Rootbeer is a nodular chert that is "tan to reddish-brown" in color (Emerson 1983). It is glossy in texture. The other form Old Blue is blueish in color. Some Old Blue has olive green bands running through it. Old blue occurs in both nodular and tabular form (Emerson 1983). |
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