14 Mercury Dimes Various Dates Fourteen Mercury dimes equal $1.40 in face value. In the precious metals world, this is a universal rule of thumb for 90% U.S. "constitutional" silver Pure Silver Content: Because it is 90% silver, each dime contains roughly 2.25 grams (or 0.07234 troy ounces) of pure silver. Targeting an Ounce: A standard troy ounce of precious metal is 31.103 grams