A friend of mine found several of these in the Tuscaloosa, Alabama area.
I have not tried to break or cut one but they are quite heavy and nonmagnetic.
Thanks,
Julian

[URL="http://i224.photobucket.com/albums/dd269/garrettjag/Rocks/IMG_0003.jpg"]

[URL="http://i224.photobucket.com/albums/dd269/garrettjag/Rocks/IMG_0005.jpg"]

Here is the photo of it