Too much bad information in this thread.
Silver
Ike dollarsAll 1971-S and 1972-S, both MS and Proof
All MS 1973-S and 1974-S
All MS 1976-S Type I dollars
Some Proof 1973-S, 1974-S, and 1976-S Type I dollars.
Put a piece of tissue paper over them. If they appear white through the paper they are silver, if they look dull gray they are coppernickel clad.
Silver half dollars
All 1964 are 90% silver
All 1965 - 1970 halves are 40% silver, all mints.
All MS 1976-S are 40% silver
Some Proof 1976-S halves are 40% silver, use the
tissue test.
Some 1992-S to 2007-S proof halves are 90% silver. Use
tissue test.
There are a few mint error pieces as well from the Denver mint from 1974 and 1977 but they are outside the realm of this discussion.