Mystery Blob In Half A Stone Concretion - Peoria, Il

[chutson99]

OK, I am new on this forum here, and here's a thing that I found and can't figure out.

This is a round, flattened hemisphere about 2.5" in diameter that appears to be half of some kind of concretion or nodule. I'm not sure about the stone it's composed of (forgive me, I'm a complete amateur and not a great geologist) but it feels flinty and shows faint concentric rings on the exterior/rounded side. The interior/split/flat side is a dark charcoal color, more porous than the exterior, and in the center is a vaguely triangular patch that is lighter in color and rougher/more irregular in relief. each corner of the triangle appears to have sort of a conical prong. I have no Idea what I'm looking at: I'm not even sure it's biological, but it looks like it might be.

I did not split this concretion open - I found it as the half you see here, already split, presumably by natural means. I found it on the surface in a ravine in a bluff here in Peoria, where the surface most places consists of glacial till piled pretty deep, so this thing's original placement is unknown. You see all sorts of rocks eroding out of gullies around here, up to big granite boulders that didn't originate anywhere nearby and that probably got bulldozed all the way from Canada by glaciation, so unfortunately, even though I know where I found it, I have no idea where it came from. I looked all around for the other half, but couldn't find it.

Here are some photos and flatbed scans of it. The file "hemisphere2.jpg" is a larger file, but I thought it would be good to include a "detail shot" for sort of an amorphous blob.

Thanks

Chris Hutson

[AgrilusHunter]

The concretion could be a siderite nodule, it looks similar to ones I've collected recently. If it is a really hard stone and an orange dust rubs off the outside surface I'd say siderite for sure. The blob is a blob. It was certainly organic at some point as it served as the nucleus for the nodule but I can't tell what it was. Similar nodules I've found like this I have identified as coprolites ... mainly because its a convenient catch all for these types of finds

Edited January 28, 2012 by AgrilusHunter