When the dollar was minted in 1878, it was the first dollar issued for American commercial use since the last Seated Liberty Dollar of 1873. The Trade Dollar was minted during this time period but was intended to be used for trade in the Orient. The dollar was continuously minted until 1904 when the supply of dollars in circulation was high and there was an absence of silver bullion. Then in 1918, the Pittman Act called for over 270 million coins to be melted for silver content. In 1921, the coinage of the Morgan Dollar resumed for that year and was replaced by the Peace Dollar commemorative that would become standard issue. Since 1921, many Morgan Dollars have been melted. Melting has mostly occurred when silver prices escalated because these dollars yield silver bullion. Although Morgan dollars were minted in large quantities from 1878 through 1904, when production ended because of a silver shortage, very few have survived until today.
Further melting occurred in the 1960s and 1980s when silver prices skyrocketed. Only about 17% of the total number of Morgan silver dollars minted have survived, and only a tiny fraction of those in Brilliant Uncirculated condition, making them genuinely scarce coins.
Mint marks appear underneath the tail feathers of the bald eagle on the reverse between the letters "D" and "O" in "DOLLAR". Mint marks include:
CC - (Carson City Mint in Carson City, Nevada)
D - (Denver Mint in Denver, Colorado)
O - (New Orleans Mint in New Orleans, Louisiana)
S - (San Francisco Mint in San Francisco, California)
*Note that the absence of a mint mark is indicative of a coin minted at the Philadelphia Mint in Philadelphia, Pennsylvania.
Of all these mints, the coins from Carson City hold more value because of their usually low mintages, as well as a western connection. All proofs for the Morgan series were minted at Philadelphia, but proof 1921-S coins are known to exist. Four special coins were struck at the Denver Mint in 1921 over a San Francisco Mint die. These four coins are known as the 1921 D over S morgan dollars.
More info and mintage details HERE.