I've noticed that if its around a lot of water it will come out black and from the soil they seem to come out shiney. I haven't found a ton though so mine may just be coincidence. Congrats on a great coin. Silver is always nice.
Great find!...and yes..Sometimes they do come out looking dark...but even then..you sorta know its not clad....But i love digging in pitch black dirt and seeing a little shimmer coming out of the hole