This is a beautiful vintage Art Deco pendant set with a large oval smoky quartz stone surrounded by marcasites. It is marked 830 which indicates a lower grade of silver than Sterling. It also has a maker's mark that I can't identify, but it is most likely German in origin. The stone has been tested and is a natural stone, not glass.
It measures 1 1/4 inches by 3/4 inch and it is in very good condition.