Concretions Concretions Boldfaced terms can be looked up in the Glossary.
Septarian concretions are a special type of concretion.
This can occur at the time of deposition, shortly thereafter, or after the sediment has hardened. Concretions in Kansas are formed from any of a number of minerals, including calcite, limonite, barite, pyrite, or silica. They vary widely in shape and size. The smallest are oolites, which can be smaller than the head of a pin. At the other end of the spectrum are the huge spherical concretions at Rock City in Ottawa County and Mushroom Rock State Park in Ellsworth County, the largest of which have diameters of 27 feet.