7.6" Polished Septarian Bowl With Ammonite Fossil - Utah

This is a beautiful, 7.6" wide decorative bowl made from septarian. The septarian comes from the Frontier Formation of Utah and was deposited during the Late Cretaceous - Cenomanian Stage, or approximately 100 million years ago. The contrast between the grey limestone, yellow calcite crystals and brown aragonite is quite stunning. This specimen also contains an ammonite cross section that can be found within the bowl.

There are cork rounds on the base of this specimen to keep it from scratching the display surface.

Septarian or septarian nodules are concretions containing angular cavities or cracks, called "septaria", filled with calcite and aragonite. A concretion is a hard, compact mass of rock that often forms around decaying organic matter. In the case of septarian nodules, the concretions formed around decaying sea-life in a marine environment.

The exact mechanism for how the cracks form in the concretions is a mystery. One possible mechanism is the dehydration of the clay-rich core of a concretion, causing it to shrink and crack. The cracks could also be caused by gas expansion produced by the decaying organic matter within a concretion. Earthquakes have also been suggested as yet another mechanism.

The cracks in the concretions are then filled in with minerals such as calcite (yellow), aragonite (brown), and sometimes pyrite, causing the very interesting patterns. They have often been described as looking like dragon's skin. They are frequently found as geodes with hollow, calcite crystal-filled cavities. More rarely, the fossils that originally started the formation of the concretion are still preserved in the septarian.
Septarian & Unidentified Ammonite
West of Orderville, Utah
Frontier Formation
7.6 x 7.3", 2.25" thick