Chert

Commonly called flint, chert is a fine-grained, noncrystalline sedimentary rock made up of silicon dioxide (SiO₂). (The mineral quartz has the same chemical formula.) Chert layers are commonly found in eastern Kansas, occurring as irregular beds or rounded nodules within limestone formations. Chert is harder than limestone and is thus more resistant to erosion. The chert-topped hills in the Flint Hills resulted from this uneven erosion of the landscape.