probably a copy
On the reverse side of the coin under the DO in DOLLAR.
1879 would make it a Morgan dollar, which has an eagle on the reverse.
The mint mark on any Morgan dollar is located on the reverse (tails) side, near the bottom, just above the letters "do" in the word "dollar."
It will have "CC" in the mint mark position, on the reverse side above the DO in DOLLAR.
The mint mark on Morgan dollars is located on the reverse side, towards the bottom, just above the letters "do" in the word "dollar."
1899 would make it a Morgan dollar. The mint mark is located on the reverse (tails) side, near the bottom, just above the letters "do" in the word "dollar."
The date 1891 would make it a Morgan dollar, so the mint mark is on the reverse (tails) side, near the bottom, just above the letters "do" in the word "dollar."
The mint mark on all Morgan silver dollars is located on the reverse side of the coin just above the letters "DO" in the word "DOLLAR".
The mint mark on Morgan silver dollars can be found on the reverse (tails) side, near the bottom, just above the letters "do" in the word "dollar."
1882 would make it a Morgan dollar, so the mint mark is on the reverse (tails) side, near the bottom, just above the letters "do" in the word "dollar."
It would be extraordinarily rare, because the last Morgan dollars were minted in November, 1921. Your coin is called a Peace dollar, as can be seen from the word below the eagle on the reverse side. Please see the Related Question for more information.
Morgan dollars were minted from 1878 to 1904 and in 1921. Any silver dollar dated 1923 is a PEACE dollar, as you can see by looking at the reverse side. The Peace design was issued from late 1921 to 1935. There's more information at the Related Question.