Just Post Strike Damage (it happened after it left the U.S. Mint). It was exposed to heat, causing the metal to bubble. Worth face value.
More information about Die Deterioration? http://goccf.com/t/317950
Retired U.S. Mint Coin Die Set information. http://goccf.com/t/302961
1988 P LMC RDV-006, 1998 P LMC Wide AM, and 2000 P LMC Wide AM. http://goccf.com/t/327834 http://goccf.com/t/294303 http://goccf.com/t/312900
1973 D Lincoln Memorial cent With Recurring Die Subsidence Error Information. http://goccf.com/t/304624
Machine Doubling tutorial. http://goccf.com/t/332421
Die states progression on coins. Scroll down, so you can see the different die state progressions. http://goccf.com/t/325638
Die Deterioration Doubling Tutorial. http://goccf.com/t/336470
Retired U.S. Mint Coin Die Set information. http://goccf.com/t/302961
1988 P LMC RDV-006, 1998 P LMC Wide AM, and 2000 P LMC Wide AM. http://goccf.com/t/327834 http://goccf.com/t/294303 http://goccf.com/t/312900
1973 D Lincoln Memorial cent With Recurring Die Subsidence Error Information. http://goccf.com/t/304624
Machine Doubling tutorial. http://goccf.com/t/332421
Die states progression on coins. Scroll down, so you can see the different die state progressions. http://goccf.com/t/325638
Die Deterioration Doubling Tutorial. http://goccf.com/t/336470