This is one of the most spectacular mint errors of all time. This proof Ike Dollar was struck at the San Francisco Mint in the 1970's on an Aluminum planchet weighing only 2 grams. It is also double struck and rotated a few degrees between the strikes. It is very well centered and shows the deep cameo portrait of President Eisenhower. It is the ultimate modern off-metal since it is on the highest denomination, in proof and on aluminum. There are only a few known U.S. coins struck on aluminum planchets. This would be the centerpiece of any U.S. mint error collection.