Gorgeous, 7.9" Septarian "Dragon Egg" Geode - Crystal Filled

This is a gorgeous Septarian "Dragon Egg" geode collected in the Betsiboka Region of Madagascar. The hollow cavity is full of shimmering, black calcite crystals. It is a hollow septarian nodule, which has been polished into an egg shape, and the natural cracked pattern of the septarian gives it the appearance of a dragon egg. There is a repaired crack that runs down that back of this specimen.

A spectacular display piece which would look great in your home/office or make a great gift for the Game of Thrones enthusiast you know. 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 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.

Calcite, CaCO3, is a carbonate mineral and the most stable polymorph of calcium carbonate. The other polymorphs are the minerals aragonite and vaterite. Calcite crystals are trigonal-rhombohedral, though actual calcite rhombohedra are rare as natural crystals. However, they show a remarkable variety of habits including acute to obtuse rhombohedra, tabular forms, and prisms. Calcite exhibits several twinning types adding to the variety of observed forms. It may occur as fibrous, granular, lamellar, or compact. Cleavage is usually in three directions parallel to the rhombohedron form.

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 is generally white to colorless and is the main source of barium.
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DETAILS
SPECIES
Septarian with Black Calcite & Barite
LOCATION
Ambondromamy, Betsiboka Region, Madagascar
SIZE
7.9" tall, 5.9" wide, 9.6 lbs
CATEGORY
SUB CATEGORY
ITEM
#124531