Photography And Half-Thoughts By Mitchell Hegman

...because some of it is pretty and some of it is not.

Monday, April 11, 2022

A Septarian Nodule

Mud is usually not super cool, but exceptions do exist.

If you have spent much time in Montana—particularly east of the Rockies—you are familiar with Bentonite.  Mixed with water, Bentonite becomes pure mud.  Some refer to it as “gumbo.”  If heavy with moisture, Bentonite is as slippery as sheer ice.  As it dries out it reaches a point where it becomes sticky and will cake onto shoes or tires.  When dry, it ranges from hardpack to chalky.

Bentonite is used as a natural sealant for ponds and reservoirs.

Bentonite also has an artsy side.  On this side, you find something called septarian nodules.  The nodules formed where ancient sea shells or other organic matter became incased in Bentonite.  Over time, the Bentonite, mixed with mineral precipitates, turned to concrete.  And the void where the organic matter resided, transformed into crystalline calcite and aragonite (in non-technical terms: pretty stuff).

Septarian nodules are found in Utah, Madagascar, and at the Helena Mineral Society’s annual rock show.

On Sunday, I found a specimen at the rock show.



Cut Septarian Nodule (The Scary Face Inside is a Bonus)



Nodule On the Outside

—Mitchell Hegman

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