@sc, I hear what you are saying about this one being different from other cents you have seen, but I would go with the assumption of chemical/environmental exposure.
If you want to really chase this down, you should consider XRF or other nondestructive elemental analysis.
"If you climb a good tree, you get a push."
-----Ghanaian proverb
"The danger we all now face is distinguishing between what is authentic and what is performed."
-----King Adz