
That's a great question, as there's a common point of confusion about the silver content in later Eisenhower dollars.
First, it's important to clarify that no Eisenhower dollars minted for circulation in 1978 were made of silver. The Eisenhower dollars that contain 40% silver were special collector's editions produced by the San Francisco Mint from 1971 to 1976. The coins minted in 1977 and 1978 for circulation are made of a copper-nickel clad composition, just like modern quarters and dimes, and contain no silver.
Because of this, a standard 1978 Eisenhower dollar from the Philadelphia (no mint mark) or Denver (D mint mark) mints in circulated condition is typically only worth its face value of one dollar. If the coin is in pristine, uncirculated condition, it might be worth a bit more to a collector, usually in the range of $5 to $8.
There were also special proof versions made for collectors at the San Francisco mint in 1978 (with an "S" mint mark). While these are also made of copper-nickel and not silver, their special mirror-like finish makes them more valuable than the regular circulation coins. A 1978-S proof Eisenhower dollar is generally valued at around $8 to $12.


