“Martian Surface” – Specimen Septarian Nodule

“Martian Surface” – Specimen Septarian Nodule

This is one of the coolest rocks I’ve ever come across, (and as a geologist for the last 15 years, I’ve seen a LOT of rocks…) it’s a type of septarian nodule.  It popped out of a concretion from the Pierre Shale in southeastern Montana.  It’s got amazing texture and gorgeous color variation and will be a great showpiece specimen on someone’s desk or display shelf.  Finally, on display it truly looks like it belongs on the surface of another planet, reminiscent of Mars given its cool iron-rich coloration.

This specimen sports deep reddish hues on top of a backdrop of off-white and rusty orange bumpy textured silt/claystone.  There are some very thin lines radiating from the center that are filled with likely either calcite or aragonite crystals.  Many of these type of concretions end up being what are called Septarian Nodules.

Septarian Nodules

We call them septarian nodules, this is a fossilized mud bubble formed between 50 and 70 million years ago composed of calcite, aragonite, and a limestone coating. These three minerals form together in a pocket of air creating a sedimentary rock concretion with a crystal surprise inside.

The word septarian comes from the Latin word ‘septum’ meaning a dividing partition between two tissues or cavities. You may connect the word septum to your nose, and you’d be right! In anatomy, the septum is the cartilage separating the two nostrils of our nose. Furthermore, the word septarian refers to the interior distinctive angular cavities or cracks separating the two halves of the nodule.

Despite being pretty commonly found concretions, these specimens are considered geological curiosities. This is due to the fact that they can form in many unusual shapes, sizes, and compositions, with varying patterns found inside.

Check out this website for more information about these cool and mysterious geologic features: (https://www.slsc.org/septarian-nodule/)

To find more fun specimen rocks we have available check out our other unique specimen pieces Here.

“Martian Surface” – Specimen Septarian Nodule