Septarian concretions are concretions containing angular cavities or cracks called septaria. The septaria are the calcite-filled cracks at the center of the rock, indicating where the centers of the concretions have shrunk. Cracks are highly variable in shape and volume. Septaria usually contain crystals, often calcite, that precipitated from circulating solutions.
The process that created the septaria remains unclear. A number of mechanisms have been proposed including the dehydration of clay-rich, gel-rich, or organic-rich cores; shrinkage of the concretion's center; expansion of gases produced by the decay of organic matter; or brittle fracturing of the concretion's interior.
Science Tuesday: The Science of Snow (December 2016) Science Tuesdays is an ongoing educational experience, offering science programming based on changing themes each month. Science Tuesdays take place throughout the day on Tuesdays at the Museum and include a variety of activities and interactive displays.