Beautiful find, I couldn't image finding anything that old. I don't think it is a recent drop either, by that I mean it being accidentally dropped by a collector or someone who happened to have it with them for some reason in the past 100 years or so. The patina looks correct for a silver coin that has been underground for a long time. Perhaps it was dropped by an early settler to the area (in the 1600's or 1700's, depending on where in Louisiana you found it) who had recently came to America. Coins were used for a long time back then, but still, 300 years would still be a very long time for a coin to be circulation. Maybe it was already dug back in Europe, giving it the color it has now, but then dropped by a collector or someone carrying it as a conversation piece more recently? Of course though, there is always that chance that some people somehow traveled across the ocean in an undocumented voyage from Europe to Louisiana in the 1400's, and accidentally dropped the coin while they were there, a little bit unlikely but possible. There were also a few Spanish explorers in Louisiana in the early 1500's, perhaps this coin could be from them? Incredible find, It's amazing just thinking about how it somehow got dropped in Louisiana.
Also, the depth of this find may give a clue as to how long ago it was dropped.
