The 1921 Mercury Dime is the scarcest coin of the series produced at the Philadelphia Mint. A total of just 1,230,000 pieces were produced, with the majority entering circulation. After the lower mintage of the issue was noted, many of these pieces were taken out of circulation and hoarded.
Along with the 1921-D, this coin is considered to be one of the semi-key dates for Mercury Dimes. Production of the denomination may have been cut short when the United States Mint focused their resources on producing tens of millions of silver dollars under the requirements of the Pittman Act.
Uncirculated examples of the 1921 Mercury Dime are scarce. Most of the pieces in existence have survived in low grades, usually not considered to be worth the grading costs (although even low grade pieces bring premiums over common coins). As a result, populations of all grades are somewhat lower than might be expected. A handful of coins have been graded MS67 with Full Bands. A recent auction for an example graded as such by NGC realized $12,650.
Well circulated pieces graded G-4, might cost around $65.