Answer: Nickel

Among all U.S. coins, there is one coin that has a curious intersection of mass and value: the nickel. The coin weighs exactly 5.000 grams per U.S. Mint specifications and has a value of exactly 5 cents.

That intersection is largely due to chance since no other U.S. coins share the arrangement and the weight of the nickel has fluctuated significantly over the last two-hundred-odd years. The original nickel, known as the “half dime”, was established by the Mint Act (a.k.a. Coinage Act) of 1792 with a weight set at 1.2 grams of pure silver (pennies back then weighed a whopping 17.1 grams and were made of pure copper).

In 1866, the nickel was overhauled and the weight increased to 5.000 grams. This had little to do with any practical consideration or the novelty of having a five cent coin weigh five grams and everything to do with the influence of industrialist Joseph Wharton on the Congress of the day. Wharton had a near monopoly on nickel production in the United States and wanted the U.S. Mint to buy up as much of his nickel reserves as possible. Although the physical size of the nickel has changed since then, the weight has remained the same.

Although the official value of a nickel has remained five cents for over a century, be careful to examine your nickels closely before dumping them in a vending machine. The rarest of nickels, the 1913 Liberty Head Nickel, has sold for as much as five million dollars (the Eliasberg specimen). Using our worth-its-weight analogy, that makes the value of the Liberty Head Nickel 100 million times its weight.