Yep, it's zinc. Looks like its been environmentally striped of it's copper layer. Yhe mottled blotchy appearance leads me to this conclusion. May have been buried at some point in it's life (in my opinion).
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Problem with this coin is I cant really tell if it was stripped or not from the pictures. The surface looks roight in the picture but I vould be wrong. Most likely stripped. Stripped or unplated would be underweight.