Please check your coin again and post a new, separate question.
The first US nickels were struck in 1866 and they were never made of pure copper.
If you have a US nickel, it is either coated with copper or has changed color due to exposure to some chemical and has no special value. If it is a 1942 Canadian nickel, it varies from $.40 to $1.75 in circulated conditions, $3 and up in uncirculated grades. The material is called "tombac" and is an alloy of copper and zinc.
The first 5-cent US nickel was made in 1866, the 3-cent nickel in 1865, and the copper-nickel flying eagle 1-cent in 1856.
All US nickels (except for silver war nickels) are 75% copper and 25% nickel, with a present melt value of 4.9 cents.
25 cents. All 1974 quarters were made from copper-nickel.
No such (US) coin exists because the copper-nickel 3 cent piece was not minted until 1865.
All 2010 US nickels were struck in the standard cupronickel alloy. A nickel that appears to be made of copper could have been discolored by heat or chemical exposure, or it might be copper-plated. The latter is a very common high-school chemistry experiment.
The only US coin ever struck in steel was the famous 1943 Lincoln cent, minted when copper was diverted to making ammunition. All buffalo nickels are made of an alloy of 75% copper and 25% nickel. Please see the question "What is the value of a 1927 US nickel?" for more information.
All US state quarters intended for circulation are made out of copper-nickel, 92% copper, 8% nickel.
US quarters didn't contain any nickel until 1965. 1964 and earlier quarters were made of an alloy of 90% silver and 10% copper. Please see "What is the value of a 1941 US quarter?" for more information.
If it is a US nickel, it is 25% nickel, 75% copper. If it is a Canadian nickel I believe it is 100% nickel.
If you found it in change your nickel is only worth face value. US nickels made from 1866 to mid-1942 and from 1946 to the present are made of a copper-nickel alloy, not silver. In fact, no circulating US coins have contained any silver since 1969.
All US half dollars dated 1974 were struck in copper-nickel. They have no added value, so feel free to spend it.