Septarian, also know as a type of Concretion, is a volume of sedimentary rock in which a mineral cement fills the porosity. Concretions are often ovoid or spherical in shape. They form within layers of sedimentary strata that has already been deposited. It is composed of a Carbonate mineral such as Calcite, a Silica such as Chert, Flint or Jasper or an Iron Oxide such as Goethite or Hematite. It is commonly found in Shale, Siltstones and Sandstones.