When was silver removed from US dollar coins?

US $1 coins were minted from 90% silver until 1935. Circulating $1 coins weren't produced again until 1971. The coins were made of copper-nickel until 1999, and were changed to the current manganese brass composition in 2000.

The denomination had been discontinued in 1935 due to low demand during the Depression, as well as its cumbersome size (38 mm and almost 27 gm). But with the coming of gambling in Las Vegas, dollar coins found a new use in high-value slot machines. Demand picked up enough that plans were made in the early 1960s to resume minting.

Even though it was clear that silver would have to be removed from coins due to fluctuations in its price, the silver lobby and President Johnson pushed for the new coins to be made out of the same alloy as before. In 1964 a test run of about 330,000 new Peace dollars was made at Denver. But when the time came to start making them for circulation, the price of silver had already increased to the point where the coins were worth far more than $1 each as scrap metal. The Mint ordered all of the trial pieces to be melted and postponed plans for any new release until 1971, when the copper-nickel Eisenhower dollar was introduced.

Rumors persist that a few 1964 Peace dollars were smuggled out of the Mint but none have ever been seen. There's agreement among nearly all numismatists that if any do surface in the future, they would be among the most spectacularly high-value US Coins ever minted.