Sweety.. Do you want to learn? Or do you want us to lie to you? I myself have been collecting and studying true mint errors and how damaged coins occur for 36 years. I'm not here to lead you astray. Nor are the other members who specialize in this field. Your Dime is nothing but environmental damage to the Cupro-Nickel clad layer. Thats 75% copper and 25% nickel. That goes for all clad coins. The copper in the Cupro-Nickel tones when exposed to a harsh environment. Many people will find similar coins with the same damage because there are thousands of them in circulation.
I can't listen to M Diamond, cause I always find my errors somewhere else, they always have an answer, but I always find it somewhere else online. Kk Ok, what do you call this 1942 nickel?
Corrosion. Most likely a harsh chemical such as acid. Also not a mint error. Here is some information that I learned many years ago. I want to share with you http://www.error-ref.com/acid-shrunk-coins/
There are so many ways all different denominations of coins can be damaged after they leave the mint. The problem with new collectors that are searching for true mint errors is that many of the coins they find are damaged or altered somehow and they make the mistake of assuming they are errors when they are not. When you first learn how coins are made, the minting process, then you will understand how mint errors occur. It takes time. We are here to help. Not every member is knowledgeable but there are some specialists such as myself that can really help you.