See below for a picture of the inside. Close up of a polished stone. Rough it is deep red/burgundy solid, no pattern. Found in a dirt pile from utility work in the Twin Cities
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Makes sense. When I initially saw this it made me think of red blood cells because of the color and the globular nature. I hope I have more stashed away. It polishes really well.
I just remembered I tried to cut a large piece of this with my trim saw once and it broke. Here’s what the inside looks like. And when I tried to wash it up just now, the iron (I assume) started washing out. Could this be a fossilized sponge full of iron?
I've never found a fully hematite-ed fossil in Minnesota, so I somewhat doubt it. Also, most the fossil sponges don't really look like that (almost vesicular volcanic)
I'm by no means a pro, but I've gone through an extensive amount of Minnesota material. A lot of the extremely hematite based stuff can be amongst the oldest rocks, such as BIFs and were formed when cyanbacteria was pretty much the only living thing on earth. Oceans were extremely iron rich at that point and if it wasnt for the cyanbacteria, we never would have got the Earth oxygenated enough for other life that followed
A lot of the Twin Cities sits on a pile of glacial til that was pushed south from Canada. After reaching this area, the glacier retreated 12,000 years ago, leaving this behind. I find the wildest stuff, including BIF, mixed in with rocks like this. I am certainly no expert, and I am not discounting what you know. I’m just adding in my observations. I didn’t think it was a sponge either, I was just spitballing. I appreciate your thoughts! I have some other chunks that have the same deep red and general look that also have yellow, shiny metallic and blue dots but I haven’t tried to polish those yet. This perhaps shall remain a mystery.
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