Carpet Rock?

[1320]

Buddy of mine discovered this today, very interesting!

 

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[Ol' Kentuck]

Neat rock. That is what's called a Septarian Concretion. Concretions are blocks of rock that form from the continued precipitation of minerals along the outer surface of the rock. They often form from hard minerals in softer rocks (such as calcite in a shale) and then when the softer rocks erode away, it leaves behind the concretion.

Septarian concretions form in a similar manner, except that they have periods of contractions and expansions which produced cracks or stress fractures within the concretions themselves. These fractures will also fill with the precipitated minerals, producing these banded concretions of different minerals. As these minerals erode, they will erode at different rates all in relation to the hardness of the mineral being eroded producing this onion effect in the rock. I've seen a lot of them around Kentucky. This one is from Russell Cave National Monument in Alabama.

It's a cool rock, but entirely natural. Neat find to add to a collection though.