This 1855 half dollar is the first piece struck by the U.S. mint in aluminum. Another would not be struck for 8 years.
This piece was brought to the collecting fraternity in an article by Wendall S. Hall which appeared on page 71 of the April 1946 edition of Numismatic Review. The piece was plated on page 73. A later article appeared in the July 1984 issue of the Numismatist where the pedigree of this piece was listed.
This unique piece was originally lot 160 in George Cogan's 5/1883 sale where it was purchased by T. Harrison Garrett. It was apparently displayed at Priceton University along with other Garrett coins and apparently was left there.
The weakness in the dentilation, especially on the left side of the obverse, shows the difficulty the mint had with this soft metal.
Photo courtesy of the "Numismatic Collection, Department of Rare Books and Special Collections. Princeton University Library."