15" Polished Septarian "Spiderweb" Sculpture - Awesome Display

This is a unique, polished section of Septarian collected in the Betsiboka Region of Madagascar. The rock in between the calcite veins in the septarian has been removed creating a spider web looking structure in the rock. The base is cut flat creating a gorgeous, free-standing display. The entire piece is 15" tall and weighs 36 lbs.

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.
Ambondromamy, Betsiboka Region, Madagascar
15" tall, 12" wide, 5.5" deep, 36 lbs