It depends on the date.
From their introduction in 1866 to late 1942 and from 1946 to the present, all US nickels have been struck in the same alloy of 25% nickel and 75% copper.
During WWII nickel metal was needed for the war effort so the Mint made special "war nickels" from an alloy of 56% copper, 35% silver, and 9% manganese. That percentage of silver weighs approximately one gram, so these coins have very little precious metal value at current (2015) prices.
A 1964 Roosevelt Dime has .07234oz of pure silver. as do all pre-1965 Roosevelt dimes regardless of date or mint mark. Those dated 1965 and later are made of copper-nickel.
around 50 cents
Pre-1965 US quarters are 90% silver with a value of about $2.50 just for the silver.
They're all worth at least $2 for their silver content.
US halves were never made of pure silver, all pre-1965 (1964 was the last) coins are 90% silver and 10% copper. From 1965 to 1970 they were made of 40% silver and 60% copper. From 1971 to the present they are 75% copper and 25% nickel bonded to an inner core of pure copper.
Pre-1965 nickels are made of the same copper/nickel blend as modern nickels. The only nickels that contain any silver are those minted during WWII.
A 1964 Roosevelt Dime has .07234oz of pure silver. as do all pre-1965 Roosevelt dimes regardless of date or mint mark. Those dated 1965 and later are made of copper-nickel.
around 50 cents
Pre-1965 US quarters are 90% silver with a value of about $2.50 just for the silver.
Pre-1965 dimes are 90% silver & 10% copper. The Actual Silver Weight (ASW) is .07234oz of pure silver.
An pre-1965 U.S. dime weighs 2.5 grams total. The silver content of pre-1965 dimes, quarters, halves, and silver dollars is 90% silver by weight, so there is 2.25 grams of silver in an unworn, uncirculated pre-1965 U.S. dime.
They're all worth at least $2 for their silver content.
If they are pre-1965 they are worth about $2.10 each in silver content, if they are dated 1965 or after, they are worth only 10 cents.
Pre-1965 silver quarters are 90% silver with a total weight of 6.25 grams, which is then 5.625 grams of silver per quarter.
A 90% silver (Pre-1965) Half Dollar weighs 12.50 grams, 1965 to date 11.50 grams
US halves were never made of pure silver, all pre-1965 (1964 was the last) coins are 90% silver and 10% copper. From 1965 to 1970 they were made of 40% silver and 60% copper. From 1971 to the present they are 75% copper and 25% nickel bonded to an inner core of pure copper.
16% of a pre-1965 silver quarter equals one gram. 17.64% of the copper-nickel quarters minted after 1964 equals one gram.