Just learning. I lean deterioration just because it's zinc. But if others think otherwise I would love to learn
Plating issue. Bubble created after it left the US Mint. It will be major zinc rot soon after. Not a mint error of any kind.
These zinc ones have those all over. A die chip is from a missing part of the die that broke off from all the pounding the die took in minting the series. This thing you're looking at is the crappy surface not adhering due to the pressure of the strike.