Septarian Nodules are ball-like structures that can be found all over the world in either very fine grained or clay sediments. Often times a shell fragment is at the center. It is composed of sandstone or clay cemented together by calcite or silica. When cut, you can see where spots on the inside shrank, to be refilled with more calcite. When polished these nodules can be used as ornaments.
The Children's Museum of Indianapolis
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