The Mercury Dime was minted between 1916 and 1945 and was designed by Adolph Weinman (1870-1952).  Also known as the Winged Head Liberty Dime,  Weinman is believed to have used Elsie Stevens as the model for the obverse of this coin. The key date to this series is the 1916 D with a mintage of only 264,000, how many have survived to this date is unknown, but there are many fakes or counterfeits out there to be aware of, and they far outnumber those that have been lost, missing, melted or otherwise. It is entirely up to you to take the chance on buying one raw.. With any key date coin it is always wise to buy one authenticated by one of the top TPGs.  If you know how to detect a fake and you have a trained eye for these things then you know what you're doing. As a novice, I wouldn't suggest spending the money to buy a key date raw....unless you know all of the things to look for.  There are tooling marks and die varieties and 4 different mintmark placements that you must look for with a loupe. (photos below).   There was four dies used for the reverse of the 1916 D Dime also....You should study those and know what they look like.  Before I dive into spending a lot of money on a key date, I buy a book on the coin and/or I read the info online from a reputable web site such as NGC, PCGS  or ANACS.  The values of the key dates in any series keep rising.  Can you take a chance on an expensive raw coin for a few thousand dollars only to find out years later that its worth nothing?   In the Virgil Hancock/Larry Spanbauer book "Standard Catalog of United States Altered and Counterfeit Coins"  it states how many of these 1916 D Mercury Dimes were counterfeited including "Sandwiching" which means putting a 1916 Mercury Dime from Philadelphia on top of a common Denver "D" minted coin and fusing them together.  There have been individuals that worked at the Philadelphia "factory" (as they put it in the book) who have altered the coin there by creating the "D" by melting and forming a "D" on the reverse, which is called "chasing" because you're "chasing" the silver around and forming a "D" into a mound to look like the desired mint mark.  Another way to detect a counterfeit coin is by the tooling marks (photo below) especially around the inside rim and around the mint mark. There are many stories of old widowed ladies cashing in on her deceased husbands prized collections to only lead to disappointment.  Its hard to tell how many raw 1916 D dimes are stuck away in old albums .  I hope this blog has informed you and at least entertaining.  The reason I wrote this is because I just bought one of these myself....authenticated by PCGS of course.  Thanks for reading 

P.S.  The photo of the Top/Bottom of the 1916 D Mercury Dime is the one that I purchased.