9.8" Polished Septarian "Dragon Egg" Geode - Black Crystals

This is a polished septarian geode collected in the Betsiboka Region of Madagascar. The hollow cavity is full of shimmering, black calcite crystals and the exterior has been polished into the shape of an egg with a glossy finish. A removable "puzzle piece" allows the interior, crystal filled cavity to be viewed.

There are repairs and spots of gap fill through both the puzzle piece and the egg, this has been reflected in the price of the specimen. Comes with the pictured display stand.

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 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 with Black Calcite
Ambondromamy, Betsiboka Region, Madagascar
9.8 x 7", weighs just over 22.5 lbs