11.5" Yellow Crystal Filled Septarian Geode (28 lbs) - Utah

This is a stunning, yellow calcite crystal filled septarian geode mined west of Orderville, Utah. Most of the material you see sold has been cut and polished, but this is in it's rough state as broken. It displays nicely without the need for a display stand.

Only the pictured side of the geode is included. Typically when these are cracked with a hammer as opposed to cut, one section will ended up being fragmented.

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.
West of Orderville, Utah
Frontier Formation
11.5 x 8.4 x 6.2", just over 28 lbs