Someone Help Me Confirm What These Might Be

[Sydneylh]

Hello everyone! I am not positive, but I thought this could be a fossilized coral of some type (chain coral, or tabulate coral maybe)? I've looked at the edges of the dark ridges under a microscope and could see tiny pores. I live in central Iowa and was searching along an eroded creek bank when I found it. Could someone help to confirm what it is or help to point me in the right direction of what it could be?

Any help is appreciated! Thanks everyone!

-Sydney

[frankh8147]

It's ironized, not coral. What you want to look for is fossils in it (not that piece but check out the location). I am not familiar with fossils in your location but in NJ, I have found some cool stuff in blocks like that. Your piece isn't showing anything on the surface so personally, I would break it open and see if there is anything inside. Don't do that until you hear some other answers though; just in case i'm wrong (but it looks like iron).

[Auspex]

It is an iron/sandstone accretion, with some small siderite/limonite concretions entrained.

[Sydneylh]

Thank you for the responses! Any advice on how I should start breaking it to see if anything might be inside of it?

[Auspex]

A whack with a lump hammer would do it, but I predict that it is homogeneous throughout.

[John K]

that has a certain cretaceous look to it....

here's a map showing Iowa Cretaceous deposits:

you'll notice some desposits in what could be considered central Iowa. I'm far from being an expert, but I've learned that if you've got cretaceous sandstones, there's a good chance of cretaceous fossils....

[Auspex]

She's mid-state, solidly in the Devonian (from which such precipitated iron accretions are not unknown; I've a couple exposures near my Camp in Northern Pennsylvania that I thought were transgressive Carboniferous until I worked out the stratigraphy).

[Sydneylh]

She's mid-state, solidly in the Devonian (from which such precipitated iron accretions are not unknown; I've a couple exposures near my Camp in Northern Pennsylvania that I thought were transgressive Carboniferous until I worked out the stratigraphy).

Hey I'm just curious, what causes the precipitated iron accretions to happen?

[Auspex]

Hey I'm just curious, what causes the precipitated iron accretions to happen?

Iron oxide in percolating ground water is often fixed by bacteria. If conditions are right, a solid mass can form as an ironstone concretion. Elsewise, it can cement sand and gravel into a mass like we see here.

Here is one case study that goes into some of the geochemistry: iron concretion.pdf

If you have trouble falling asleep, this will help!