This appears to be made of brass and measures just about 1" square by 1/4" thick. It's in a book form with etched designs front and back. I'll do my best to try and zoom in on the photographs inside since 1 solder looks to be of high rank. I believe the type of photos inside this locket are called Ambrotype. The first of 4 photos inside this little locket looks to be newer than the other 3 soldiers.