What this coin looks like (obverse, reverse, mint mark location, special features, etc.):
The 1979 Type 2 Clear S Washington Quarter has a much clearer and well-defined S mintmark and is also only found as a proof coin. Depicted below is an example comparison image between the type 1 filled "S" vs type 2 clear "S":
Coin valuation chart: Typical coin prices, values and worth per grade or condition - in USD