This is the unique 1846 quarter eagle trial struck in copper. This famous trial is also a mint error - one of only 5 or 6 significant pattern mint errors known in the entire pattern series.
After being struck as a quarter eagle, the coin appears to have been placed on top of a half eagle planchet and was then struck by half eagle dies. This is known as a piggy-back rider error. The coin was aligned such that the half eagle obverse was struck over the reverse side of the quarter eagle die trial. Although the quarter eagle obverse was flattened by the half eagle planchet underneath, both dates are clearly visible.
This unique piece is ex 52 ANA lot 4478, 58 ANA lot 469, Bowers and Merena 5/93, Mike Byers as PCGS62BN, Heritage 1/07 as NGC65BN, Simpson collection - PCGS65BN.
Photo courtesy of Mike Byers.