It's just some kind of Environmental Damage.. Exposure to some chemical. I have found hundreds like that over the last 8 years of Metal Detecting!
You can make nearly any coin look like that if you've got the right chemicals. The Zincoln's special talent is that "the right chemicals" are just air and moisture.
Not just pennies.. All coins! This was today.. 5 hour dirt hunt - Singular - penny Plural - pennies.. Not penny's
I'm have to invest in one of those. And bro I know the plural word for penny's I just to lazy and phone has alot cracks just like I spell people ppl