Brownishbeard
Tenderfoot
I live in minnesota. I was digging a hole to plant a tree in some relatively sandy and clay mixed soil. The shovel created a sort of cross section in the side of the hole when I noticed this rock about 2 feet down from the surface with a rust colored streak in the sand, verticly above it that went about 4 inches long. I thought it was iron due to the color, but it is not magnetic, and my metal detector does not acknowledge it. I sanded one side flat to get a cross section of the rock, only to find that it appears to be metallic and can be polished to a mirrored surface but after a few days oxidized or patinaed over to a black or grey color. The rock does conduct electricity. Pictures show both sides as well as befor and after I sanded and polished it. It weighs about 8 grams. I have no idea what it is.
Depending on the amounts of sulfide and arsenic they can be fairly reactive to air and oxidize quickly when freshly broken or polished as you have done. One characteristic is a burnt match smell when scratched or broken.
