rare
lightning stone
septarian nodule · no lightning in it
The tell
A network of pale cracks filled with a lighter mineral, running across a darker body like lightning or a cracked mud flat.
The cracks opened inside the nodule while it was still shallowly buried, as the gel-like middle contracted and squeezed its water out. Nobody fully agrees on the mechanism. Calcite filled them afterward. Pier Cove to South Haven is the belt.
What it gets mistaken for
- black shale
- limestone
- septarian nodule
- concretion
- turtle stone
The facts
- also calledseptarian nodule · no lightning in it
- age~350 million yrs
- where it turns upSouth Haven, Pier Cove · SW Lake Michigan
- the field markcracks filled with pale calcite that fizzes
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