One person told me zinc rot, another with more experience said possible retained cud. Close up of obverse is to show opposite side where damage is. Not listed on cuds on coins. Doubt I will send him anymore pics, after he said the MIE on reverse of quarter wasn't big or interesting enough.
I see nothing that has to do with a CUD.. All I see is a plating issue due to Die Deterioration. And maybe some damage due to circulation.
Of course it's a chip, cuds are only on the rim. They list die cracks, BIE's, retained cuds. Same as the BIE that they list.