Not sure what this is, but thought some of you may know what this is. The reverse shows what looks like a head feather sticking out of the back of the eagle head. There looks like there is also some raised area on the eagle's beak right where it splits top and bottom. Don't know if this is die issue or silver debris that got smushed in the die when struct? Have a look at the photos:
It does look like a crack and chip. https://www.error-ref.com/interior-die-break-connected-to-die-crack/
The 59D has a DDR with a heavily cracked die on the Eagles mouth, and across the neck. Yours could be a later die stage. Please post a good pick of the obverse for die markers.
Have you checked the die crack from forehead thru the hair. They are markers to identify a variety. http://www.varietyvista.com/09b WQ Vol 2/DDR Detail Pages/1959DDDR001.htm