4.4" Polished Septarian Egg with Base - Madagascar

Polished Septarian Egg with Base - Madagascar #118138

This is a beautiful hand polished egg and stand that were both formed from septarian. The septarian comes from the Betsiboka Region of Madagascar and was deposited during the Jurassic period. The polishing reveals a beautiful pattern of the yellow crystals. The polished septarian base has a concave depression that the eggs sits upright within.

The egg itself is 4.4" tall and including the stand the entire specimen is 5.5" tall by 6.3" wide.

Septarian or septarian nodules are concretions containing angular cavities or cracks, called "septaria" which have become 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. 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 suggested as yet another mechanism.

The cracks in the concretions are then filled in with minerals such as calcite (yellow) and aragonite (brown) and sometimes 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.

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