I got one of these off of Go'Bhu Gascon as well. Is there a specific quest that they're associated with, or does anyone have an idea what can be in the chests (anything besides a "Sphene")?
Interestingly enough, I was doing M10 with my LS tonight and had this key from the same NM that drops the Augery Shells, though I honestly cannot remember his name. Interesting stuff!
ok after 2 weeks of having the key, i finally got frustrated with its use of an inventory slot and decided to go out treasure hunting. I found the chest in J-7 and it contained a "Sphene" (a yellow jewel). I found a map with the treasure locations here: http://www.speakeasy.org/~sticks/ffxi/treasure/Mp_Beadeaux_01.html