This is a spectacular One Dollar Silver Eagle mated pair struck at the Philadelphia Mint in 1986. It was incredible that both pieces of this mated pair were released together and still survived. A 3M sanding disk adhered to the lower die and was struck into the reverse of the blank planchet. It has the same diameter as the struck coin, fits very snug and locks into place.
There are five or six U.S. Silver Eagles known to exist with either the obverse or reverse 100% struck through a 3M sanding disk. Until this actual sanding disk was discovered struck by the reverse die and mated to this struck-through coin, it had not been determined what these Silver Eagles had been struck- through.
The strike on the sanding disk is incredibly sharp and has a surprising amount of detail considering that it is not metal. This dramatic mated pair is one of the most unusual major mint errors ever discovered.