It's a coin that was minted at the New Orleans Mint. That facility operated from 1838 to 1861 and then again from 1879 to 1909.
To find out the value of a specific coin minted there you'll need to post a new question with its date.
26.73 grams.
The "O" mint mark is from New Orleans
As of 4/12 a 1898 O Morgan silver dollar in MS-65 condition is worth $238.
Please look at the coin again and post new question. With the date of 1839 it can't be a Morgan dollar. The Morgan dollar was first issued in 1878.
A rare Morgan Silver Dollar is 1876.
The Morgan silver dollar is a collectors item and can be about $39
Neither. The Morgan silver dollar is 90% silver, 10% copper.
The 1901 Morgan with no mintmark is worth more than the one with the "O" mintmark, but the difference depends on the condition (grade) of the coins. A 1901-O Morgan in the grade of EF-40 has an average value of $29.00 A 1901 Philadelphia (no mintmark) Morgan in the same grade is $105.00.
The 1881-O (New Orleans) Morgan is common, retail values are $17.00-$26.00 for circulated examples.
An 1879 "Silver Dollar" is a Morgan dollar.
The Morgan dollar is 90% silver, or contains about .77 troy ounce of pure silver.
The O is the mint mark, it stands for the New Orleans mint.