Day #6 Deskcrop: Weathered Pyrite Nodules

The UPS delivery man dropped off a package at my office today, and he had a rock question for me to answer, as well. His friend had found a dense rock, nonmagnetic, with an odd pattern of clustered corners on the surface. Could it be a meteorite?

Sadly, no. But I had a deskcrop that fit that very description, collected in western Kansas, too. He agreed that this was indeed (most likely) what his friend had found.

Weathered Pyrite Nodules

It turns out that these pyrite intergrowths are not uncommon in the chalk beds of the Cretaceous Western Interior Seaway that crop out all around this part of western Kansas. They weather to a rusty brown (limonite/goethite?) on the surface, but maintain their intergrown cubic crystal forms. One of these days I’m going to try to clean the tarnish off of one of these and see if I can display the fools gold within.

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