Pre-1964 quarters in the United States were made of 90% silver and 10% copper.
U.S. quarters dated 1964 or earlier contain .18084oz of silver.
Yes, the reason why quarters (and dimes, and half dollars) dated 1964 and earlier are worth more than their 1965 and later coins is because they are 90% silver.
40 x 6.25 = 250 grams, ~8 ounces.
25 cents, unless they are date 1964 or before, then they are 90% silver.
64 and earlier.
16% of a pre-1965 silver quarter equals one gram. 17.64% of the copper-nickel quarters minted after 1964 equals one gram.
In unworn condition, 6.25 gm. Current copper-nickel quarters weigh 5.67 gm.
At present, pre-1965 US quarters have a melt value of just over $5. That doesn't take into account possible collector value though. For specific values, post new questions about specific dates.
U.S. quarters, starting from 1932, are called "Washington quarters." Washington quarters dated from 1932 to 1964 are made with 90% silver and 10% copper, and weigh 6.25 grams. The value of the metals depends on the market price of silver and copper. As of October 5, 2007, the value of the silver in a pre-1964 Washington quarter is $2.41 (market price of silver $13.39 per ounce) and the value of the copper in a pre-1964 Washington quarter is about a half of a cent, giving the total value of a pre-1964 Washington quarter about $2.42. If the coin is rare, and/or is in mint like condition, it could be worth significantly more. None of the 1944 Washington quarters (Philadelphia, San Francisco, and Denver mints) are rare, but if the coin is in mint state, it would be worth about $35.
US quarter dollars issued through 1964 were 90% silver. Quarters issued from 1965 onward (except for some proof coins made for collectors) contain no silver.
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