there is no such thing as 100 percent sterling silver..if it was it would be too soft..however, it is within the guidelines of .925 sterling silver..and it fall's into the 90 percentile range..which is what a good quality necklace is made of...and the clasp is welded on...which is another sign of a quality...if you look up these 2 factor's on the net..you can have a better understanding of the make up of ..925 sterling silver...that is a good question...also look up the make up of a quality chain...these research site;s can give you much information about purchasing..and what to look for...thank you,,,that is an excellent question....and no, it will not rust...