Aquamarine is my birthstone :) I wish there were more photos of it...is the back solid silver or open back? how large is the bale? a photo next to a dime or quarter or penny would also help.
Here are some extra pictures for your review :-). Please edit out any spaces in the URL. http://www.flickr.com/photos/31069197@N06/sets/72157627234209093/
The person I bought it from told me it was Aquamarine. Of course not being an expert myself, I wouldn't be able to say with 100 percent certainty, all I can do is go based on what I was told. It may very well be topaz, I don't really know :-(