Assuming you are describing an Eisenhower dollar, a cupronickel* circulation coin would sell for face value or slightly above. A proof version of the coin would sell for 2 or 3 dollars.
(*) Even though they are called "silver" dollars, circulation $1 coins made since 1971 have all been made of either cupronickel or manganese-bronze. They do not contain any precious metals.
There is no silver in a 1972 US half dollar.
$1
A 1972 silver dollar, known as the Eisenhower dollar, weighs about 24.59 grams. It is composed of 40% silver and 60% copper.
No half dollars intended for circulation minted since 1970 contain any silver. No 1972 half dollar has any silver. It is only worth 50 cents.
It's worth one dollar.
Current retail value is $6.00
This would be the 1972 Silver Eisenhower dollar variety from the San Francisco Mint. In uncirculated condition, it would be worth about $8 and if you have a Proof coin, it would be worth about $9.30.
The 2012 American Silver Eagles coins are one ounce of pure silver.
If you got it from a bank or in change it's just a dollar and it has no silver in it. Some collectors coins were struck in 40% silver but were not released for circulation.
With the date of 1979 it's just a Susan B. Anthony dollar coin and has no silver in it so spend it.
None. It is copper-nickel. Half dollars stopped containing any silver after 1970 for circulation issues.
If you mean a American Silver Eagle dated 2000, it's one ounce of pure silver.