Is this a die chip? Can't imagine what else it could be. Kind of crusty, but interesting none the less.
Looks that way . I just couldn't find it though .http://cuds-on-coins.com/lincoln-cent-idb-1959-2008/
Can you take a picture of the whole coin? That is only one of 3 things it shows you still need these two it has to be a %100 match for all.
The year 1957 was known for Die Chips on the B and on the number 9. They don't all look the same because of different stages of the Die Deterioration. I have about a dozen in my collection Here is one from my collection -
Try the Wheat Cents listings http://cuds-on-coins.com/lincoln-cent-interior-die-break-1909-1958/ You posted the Memorial Cent listings.