Any idea about this?

[sammerguy]

I found this while walking in the woods awhile back. The outside is weakly magnetic and the inside is stone of some variety. I accidentally broke it when it was dropped. To my suprise the stone was not attached to the outside, just resting in the casing.

http://www.flickr.com/photos/9398026@N07/5508818589/

http://www.flickr.com/photos/9398026@N07/5509417134/

[Eu_citzen]

I'm thinking Limonite, does it leave a yellowish to brownish streak on a unglazed porcelain?

[sammerguy]

Maybe, but i guess im wondering why it has a metallic shell around it. It was totally encased at first.

[2Minnesota]

This is just a guess, but these rocks are common where we look for agates. The first time I found one I thought it was a petrified egg--I was very young!

I've been told they are iron ore? Again not an expert but.....

[claymation]

I think it's a concretion. Probably iron sulfide or iron oxide shell. They are like moki marbles.

[jadeblackhawk]

Those things are all over michigan. We used to break them open and use the insides for drawing chalk as kids.