It is very important to first weigh your coin to make sure it is the weight of the planchet one thinks it is. If it looks silver then it must weigh the same weight as a silver planchet. Also, a coin needs to be tested by an XRF device, some dealers and refineries use them, but you can also contact PCGS or NGC and they will test them.
There’s a lot of plated and altered coins in the “wild” so it’s important to weigh your coin and have it tested. Also, just because a coin is a little over weight or under weight doesn’t mean it’s a mint error or an off metal planchet.