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Pyrite Concretion, Indiana

Submit an Entry: My Concretion and Its Story

By Greg_McHone

Pyrite Concretion, Indiana

Pyrite egg, a concretion in limestone (penny for scale)

Where I Found It

south-central Indiana near Shelbyville.

How I Found It

A land owner brought it to me for identification, along with a collection of similar round concretions. He invited me to his property, where it became evident that the concretion was one of several scattered in crushed limestone brought in to repair his driveway. So it is likely from a local quarry. All were masses of iron sulfide, or pyrite, and as happens for this mineral, the owner hoped it might be valuable. For my efforts to explain its origin, he gave me one of the nicest egg-shaped examples.

Advice

  • Pyrite is a common and often attractive mineral, but usually it occurs in cubic crystals or aggregates of cubes. Less common is this concretion form, which might have formed in limey seafloor mud, before it lithified to limestone. I keep it to display in a collection of stone eggs, most of which are cut and polished to their shape. Not this one!

Andrew Alden, About.com Geology, says:

That is a splendid example, one that might prompt me to order a yard of crushed stone from the same supplier. The square faces of the cubic pyrite crystals are nicely presented in this specimen.

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