Limestone (ecronite)

Limestone crinoidal

Crinoidal limestone (ecronite)

Biogenous sedimentary rock.
This sample is a fossiliferous limestone dominated by crinoid stem columnals and trilobite fragments. Crinoids are any of a large class (Crinoidea) of echinoderms usually having a somewhat cup-shaped body with five or more feathery arms attached to a columnar stock that attaches to features on the seafloor. Such crinoid-rich limestones are called encronites. The calcerous disks of their columns consist of crystalline calcite. These disarticulated fragments acumulate like sand grains associated with fossil "crinoid garden" deposits). Late Ordovician, Kope Formation, Cincinnati, Ohio. 2/2/2021