Welcome to CT. The dime has suffered environmental damage. Probably spent time in the dirt. Not a mint error.
The clad layer on your coin is a mixture of 75% copper and 25% nickel. Copper turns brown with exposure to most things.
Yes to Environmental Damage This is a Mint Error. Missing Clad layer usually only occurs on one side of a clad coin.. From my collection -
Most likely environmental damage as explained in this thread. To be sure, you can start your own thread and post pictures.
2.27 grams is the correct weight for clad dimes 1965 until present. Environmental damage will make the 75% copper layers show as dark copper color. And welcome to CoinTalk