What this coin looks like (obverse, reverse, mint mark location, special features, etc.):
One major variety of the 1878 Morgan Silver Dollar features 7 Over 8 (7/8) Doubled Tail Feathers. The initial die originally had 8 feathers but was later changed to 7. This resulted in what looked like 7 feathers struck on top of 8 feathers - and gave it a doubled feather look. The difference between the 7 Tail Feathers vs 8 Tail Feathers vs 7/8 feathers is depicted below in the example comparison image:
Coin valuation chart: Typical coin prices, values and worth per grade or condition - in USD