Unidentified stone artifact
September 6, 2007 2:39 PM   Subscribe

Geology/ArchaeologyFilter: What is this stone? Is it man-made? Is it natural? How old is it? Who made it? Should I donate it to a museum?
posted by billtron to Society & Culture (11 answers total) 5 users marked this as a favorite
Well it sure as heck isnt natural. I'm not familiar with specific archaeology outside of the western US, but it doesnt look like a millingstone or anything like that.

As for its antiquity, I suggest you find a local museum/university and see if they have some idea.

Neat looking though.

Where'd you get it, if I may ask?
posted by elendil71 at 3:07 PM on September 6, 2007

Looks to me like the outer part is volcanic. Parts of Southern Utah are littered with similar looking material that has emerged from eroding sandstone that once encased it.

I can imagine that your object could be similar. An unusually shaped fragment of a volcanic bomb got burred and filled with sand or other sediment. As more material accumulated, time, heat and pressure fused the sediment. Erosion eventually exposed it, but the hard volcanic rock protected the inner sediment. However, over time, water has penetrated along the inner margin of the volcanic rock, softening the sediment at the margin so that it has eroded more quickly.
posted by Good Brain at 3:08 PM on September 6, 2007

I may be wrong about the volcanic origin. The outer shell may be an iron concretion.
posted by Good Brain at 3:21 PM on September 6, 2007

Response by poster: elendil71, I found it in Pike County, Ohio.

Good Brain, that seems like the most reasonable explanation. I was worried I had another Ohio Decalogue on my hands!
posted by billtron at 3:26 PM on September 6, 2007

Your rock is completely natural and definitely not museum worthy, I hate to say, but that doesn't make it any cooler. It's a type of rock sometimes called an ironstone. They are also called iron concretions, where sandstone makes up the inner part of the "ball" and a thick rim of an iron mineral called hematite makes up the outer edge. Some geologists classify them differently, but both come in different shapes and sizes, some amazingly round, and both are formed by water that permeates the porous sandstone and through a chemical process called reduction, forms bands of iron minerals as reducing water carrying iron meets oxidizing water and the iron is precipitated out - in other words it gets rusty!

This process takes a very very long time and an amazing amount of water. Eventually the rock that houses the iron stones or concretions appears at the surface, and weathers. Most of the sandstone weathers away and sometimes leaves these odd artifacts behind. Sometimes the sandstone nodule within the much much harder iron rim remains, sometimes not. In your case a little eroded away.
posted by barchan at 3:32 PM on September 6, 2007 [3 favorites]

Dang it, that's what I get for not previewing. Sorry, Good Brain.
posted by barchan at 3:33 PM on September 6, 2007

billtron, just so that you can see for yourself, there are concentric rings in the outer rock that are the same shape as the inner. That's a pretty easy way to determine that it's natural.

That is a very sweet sample and I would give it to an elementary school or middle school. Anything that looks that cool is a great asset to science teachers. (Kids dig that stuff!)
posted by snsranch at 5:08 PM on September 6, 2007

Argh, *less* cooler, *less* cooler. And seconding snsranch.
posted by barchan at 5:37 PM on September 6, 2007

Can you take some more detailed macro pictures of the corners? If it has iron in it then a simple magnet test will determine that. Is it heavy like a stone of the same size or heavier?
posted by JJ86 at 8:35 PM on September 6, 2007

JJ86: It's a hematite, which has too much oxygen in it and odd enough atomic structure, or crystal lattice, to be anything other than weakly magnetic. ("Hematite" gemstones that have magnetic properties are all simulated hematite that has been magnetized - scratching them on a raw ceramic plate will leave a gray streak whereas true hematite gives a reddish brown streak. True hematite cannot be magnetized.)
posted by barchan at 9:17 PM on September 6, 2007

Response by poster: Thanks for the information, everyone.

I received an email from Gregory Vogel, the director of research at the Center for American Archaeology in Kampsville, Illinois, and he directed me to this website on Liesegang Rings that seems to explain the phenomenon fairly clearly and has lots of photographs of similar rocks all bunched together in a calendar-like formation.
posted by billtron at 12:12 PM on September 7, 2007

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