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There's no way to give a specific answer without knowing any details about the coin such as date, mint mark, and condition.
The letter is known as the mint-mark and tells where the coin was made. A coin having a P mint-mark (or no mint-mark on some coins) was made in Philadelphia, a coin having an S Mint-mark was minted in San Fransisco, a coin with a D mint-mark was minted in Denver.
Unless it has an O mint mark, about $300 for its gold content. If it's a 1909-O, it's worth about 2.5X as much as a collectible coin.
The mint mark is located on the reverse [tails] side of the coin at the bottom below the wreath. If there is no mint mark then the coin was minted at the Philadelphia Mint.
There is not always a mint mark on coins. If your coin does not have a mintmark it means that it was made at the Philadelphia mint in Pennsylvania.
Assuming no mint mark this coin has a retail value of $4.00 to $6.50 in collectible circulated condition with a bullion value of about $4.00.
Assuming the coin is circulated and still in collectible condition, the 1890 Morgan is a common coin, current average values are $38.00-$44.00 depending on the grade of the coin.
It depends on the type of coin the date and denomination on were the mint mark is located
No US coin bears an "F" mint mark
Mintmarks identify which mint the coin was made at.
The mint mark of the Denver Mint (shown as a "D") and the San Francisco Mint (shown as "S) on the Eisenhower Dollar is located on the obverse (heads) side of the coin directly beneath the bust of Eisenhower. If there is no mint mark there, then the coin was struck at the Philadelphia Mint and in this mint did not place a mint mark on the coins struck there until 1979.
A mint mark is a smaller letter or letters representing the mint facility the coin was struck and are found in various places on the coin.