Non- clad coins weigh less than a normal coin, so, check a coin if you suspect it of being a mint error. However, with your coin, it is clear that it was in the ground possibly for all 12 years of its existence. Environmental damage means a coin oxidizes, or interacts with chemicals/moisture in the environment. https://www.ngccoin.com/news/article/5630/NCS-conservation/
Environmental Damage is the complete name for it. Here are examples of Clad coins a d even Nickels I have detected over the years -