1. Condition: The condition of a coin is one of the most important factors in determining its value. Coins in mint state (MS) are worth more than those with wear and tear.
2. Rarity: The rarity of a coin also plays a role in its value. Some 1921 silver dollars are rarer than others, and therefore worth more. For example, the 1921 Morgan silver dollar is rarer than the 1921 Peace silver dollar.
3. Mint mark: The mint mark on a coin can also affect its value. Coins from certain mints are more rare than others, and therefore worth more. For example, 1921 silver dollars from the Philadelphia mint are more common than those from the Denver mint.
4. Variety: There are different varieties of 1921 silver dollars, each with its own unique characteristics. Some varieties are rarer than others, and therefore worth more. For example, the 1921-S silver dollar with the "VAM-1" variety is more rare than the standard 1921-S silver dollar.
Here is a general guide to the value of 1921 silver dollars:
* 1921 Morgan silver dollar (common date): $25 - $50
* 1921 Peace silver dollar (common date): $20 - $40
* 1921-S Morgan silver dollar (semi-key date): $100 - $200
* 1921-S Peace silver dollar (key date): $200 - $300
* 1921 silver dollar with rare variety: $500 - $1,000 or more
It's important to note that these values are just a general guide and can vary depending on the specific coin and market conditions. If you are interested in selling a 1921 silver dollar, it's best to get it appraised by a professional coin dealer to get an accurate estimate of its value.