Septarian concretions or septarian nodules are sometimes called Dragon Eggs. They form primarily in an ocean setting just below the sediment surface through a series of steps. Some sort of nucleus, such as a fossil, is buried in the sediment. Fine grained calcite mud precipitates around this nucleus and a hard mud ball is formed. The longer the ocean level stays relatively constant, the bigger the mud balls become. It is believed that bacteria re responsible for precipitating the calcite. These mud balls are called concretions. Over time these mud balls get buried deeper under more and more sediment. Pressures from overlying sediment or uplift of the rocks at a later date causes these mud balls to crack. Fluids flowing through the cracks precipitates crystals inside the cracks. These cracks are referred to as septa, which means wall or fence in latin.
The minerals that are precipitated in the fractures can be variable depending on the composition of dissolved elements in the water flowing through them. Different locations can have different minerals and different colors. At Orderville, Utah, the main minerals that are present are honey colored calcite and brown aragonite. The aragonite forms a margin along the fractures and the calcite fills into the fractures. Sometimes openings remain within the fractures and this creates small geodes with beautiful crystals in them. Occasionally the fossil that was the nucleus for the concretion is still visible.
These slabs have been stabilized with butvar, a museum grade consolidant. This will help to hold together the rock along fracture weaknesses. This technique is described in my article on stabilization or my youtube video.
The slabs have been drop tested, which means they were dropped onto a hard surface to ensure they did not break apart.