I am looking for any sort of information that I can find about this pin. It only has "Sterling Silver" stamped on the back. No other markings. There are two stones missing.
There's a website devoted to sterling silver (jewelry and other objects) that has what looks like a reasonably active forum. You might want to see if anyone on that forum can help you: http://www.925-1000.com/forum/index.php?
This pin is set with marcasite, which is really pyrite, cut into small faceted gems.
Marcasite was once called "poor man's diamonds" because it was affordable. It is almost always set into sterling.
This type of jewelry was popular for a long time, but I can't say exactly how old your pin is-it may date from the 1890s all the way to the 1930s. The old-style pin back may be a clue that it is around the turn of the century. There was also a revival of antique-style marcasite jewelry in the 1980s.
I would polish it carefully with a treated jewelry cloth to shine up the silver a little. It should retain it's dark patina.
Do not put it in water, as the marcasites are glued in.