Septarian sphere
93 MM
Septarian Nodules formed during the Cretaceous Period (50 to 70 million years old) when the area was covered by the ocean. Mud balls formed around the sea life killed by volcanic due to chemical reactions. As the ocean receded, the balls were left to dry and crack. Because of their clay content they also shrank at the same time trapping the cracks inside. As decomposed calcite from the shells was carried down into the cracks in the mud balls, calcite crystals formed. A thin wall of calcite was transformed into aragonite separating the bentonite heavy clay exteriors from the calcite centers.
Septarian nodules are composed of Calcite (The Yellow Centers), Aragonite (The Brown Lines) and the Outer Grey Rock is Limestone. Occasionally the fossil or some of the fossils which started the formation of the rock is noticeable in the rock.
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