That is what economists call a "bi-metallic standard" as opposed to only a "gold standard" or "silver standard." Since our nation's economy, and a great many other countries, used a bi-metallic standard for huge portions of our history how well did it function?
Rick Kelo notes that, "Bimetallic standards are inherently flawed because people tended to arbitrage the lower valued metal so the nation was always on either a de facto gold or a de facto silver standard. If gold was actually worth a little bit more than silver, but the country's set exchange rate for trading in paper bills for either metal differed from the true value, then people noticed this. They would redeem currency in the under-valued metal, then take it across borders and sell the metal at its higher market value." Richard Kelo continues, "This has been evidenced in every country to ever adopt a bimetallic system and is known among economists as 'Gresham’s Law.'"