Some would call this a faux moon stone but I believe it is a thermal plastic they used in the 1950's. It is a very soft blue and will compliment your tie. It is a slide bar that measures 2" in length with width of stone at ½". There is no maker's mark on this piece. I also have some cufflinks that match this tie bar that is on this site.
Tie clips are designed to keep men's ties straight and neat without damaging the tie or shirt fabric. The tie clip surged back into acceptability amongst gentlemen with style and flair.