Button with seal of Francis I, King of France

This is a metal button, possibly silver, that appears to be very old. The seal is Francis I, King of France who ruled in the 1500's. It is a salamander with a crown. The wording around the edge is "FRANCISG DC FRANCORREX" with a Roman cross. This is the best I can tell. Any info on this button you can give me would be much appreciated. I have no idea where this button came from.