How Much Is This Worth?

Ballpark of $15-20 though would need solid pictures for a good estimate, especially if it is in better condition then you think.

That is assuming you are in the US.

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Below is a link to a reasonably good retail price guide. The value of your 1891-O Morgan dollar will vary depending on just how much wear it has as a result of circulation and whether it has any damage.

http://www.numismedia.com/fmv/price...icesgd.shtml

(The "G4" column is for a coin with a great deal of wear, the "AU" columns are for a coin with a barely detectable amount of wear. These "retail" values are what you might expect to pay for it at a coin dealer; selling it to a dealer will bring much less, along the lines of the price Napoleon mentions.)

There are also collectors who specialize in Morgan dollar varieties (referenced by " VAM" numbers), so even though this is a fairly "common" date, there is a slight possibility of additional value due to it being a more uncommon variety. Detailed pictures will be required for our VAM specialists to determine if it is a more valuable variety.