Mercury Dime

A few days ago I noticed a strange dime sized silver coin in my change purse.  When I had a chance I looked at it more carefully.  It was very worn and I didn't immediately realize it was American.   However I eventually figured out it was a Mercury dime.  These were minted from 1916 to 1945.  My coin is dated 192?, perhaps 1920 with only the top left curve of the 0 still apparent.  It looks something like this but even more worn.  I must have received it in change fairly recently.  This is unusual as although the coin is too worn to have much value to collectors it has a silver value of about $1.15 and most such coins were removed from circulation long ago.  It is interesting to speculate on its history.  It obviously has been circulated heavily but presumably not recently or someone would have recognized it (as I did) and set it aside.  So my guess is it was out of circulation for a long time and then recently found and spent by someone who didn't recognize it as rare.