What this coin looks like (obverse, reverse, mint mark location, special features, etc.):
The 1918/7 S Standing Liberty Quarter had a major overdate error. The 1918 date was struck over and on top of an 1917 date. This resulted in a prominent error where the underlying "7" is seen clearly within the "8". An example image of this overdate error is depicted above.
Coin valuation chart: Typical coin prices, values and worth per grade or condition - in USD