Metal Composition: 97.5% Zinc - 2.5% Copper after 1982
Diameter: 19 mm
Mass / Weight: 2.5 grams
What this coin looks like (obverse, reverse, mint mark location, special features, etc.): Some 1990 S Lincoln Memorial Cents (Pennies) did not receive an S mint mark on the coin. These are extremely rare and valuable. The San Francisco Mint produced only Proof coins and this error coin is also a Proof coin so we know it came from the San Francisco Mint but the S mint mark is absent.
Coin valuation chart: Typical coin prices, values and worth per grade or condition - in USD