(Wikipedia)
In the last hundred years, the face value of circulation coins has usually been higher than the gross value of the metal used in making them; exceptions occurring when inflation causes the metal value to surpass the face value, causing the minting authority to change the composition and the old coins to begin to disappear from circulation (see Gresham's Law.) However, this has generally not been the case throughout the rest of history for circulation coins made of precious metals.
Exceptions to the rule of coin face-value being higher than content value, also occur for some bullion coins made of silver or gold (and, rarely, other metals, such as platinum or palladium), intended for collectors or investors in precious metals.
En plus il me semble qu'il est interdit de détruire de la monnaie.