This is one of the most dramatic and unique major mint errors ever discovered and has been well known in the numismatic community for decades.
It is an Indian Head Cent double denomination with different dates. An 1859 Indian Head Cent was struck over an 1857 Seated Half Dime.
This mint error may have been deliberately made. Only the obverse of an 1859 Indian Head Cent Die was used. It was struck over the obverse of the 1857 Half Dime. The reverse of the Half Dime is slightly spread out since the most likely scenario was that this Half Dime was placed on top of an Indian Cent blank planchet prior to being struck by the obverse Indian Cent die.
This mint error ranks at the top of the list of the most spectacular mint errors of all time.