6.4" Polished Septarian Geode Sphere - Madagascar

 
 
This is a stunning 6.4" wide, polished septarian geode collected in the Betsiboka Region of Madagascar. The hollow cavity is full of shimmering, black calcite crystals and transparent barite crystals.. It is a hollow septarian nodule, which has been polished into an round, sphere shape.

Septarian or septarian nodules are concretions containing angular cavities or cracks, called "septaria" which have become filled with calcite and aragonite. A concretion is 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. Another is the cracks being due to the expansion of gases produced by the decay of organic matter within a concretion. Earthquakes have also been a suggested as yet another mechanism.

The cracks in the concretions are then filled in with minerals such as calcite (yellow) and aragonite (brown) and sometime pyrite causing the very interesting patterns, which have often been described as 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.

Barite, commonly spelled baryte, is well-known for its great range of colors and varied crystal forms and habits. It is a heavy mineral consisting of barium sulfate, and typically has the chemical formula of BaSO4. The barite group consists of baryte, celestine, anglesite and anhydrite. It's generally white to colorless and is the main source of barium.
FOR SALE
$175
DETAILS
SPECIES
Septarian with Black Calcite & Barite
LOCATION
Ambondromamy, Betsiboka Region, Madagascar
SIZE
6.4" wide, just under 11 lbs
SUB CATEGORY
ITEM
#134430