Unplated Zinc planchet or coin occurs when part of the planchet coil stock is not plated and then punched out as a blank. The blank makes it through the entire minting process and leaves the mint as a struck coin without the plating layer.
These should be checked by an expert since some use chemicals in an attempt to remove the plating artificially.
Unplated zinc planchets range in value from $100 to $200 and some can be worth more based on the condition, grade and date. Although none can exist for US Lincoln Cents before 1982.
Related link: Missing clad layer