Antique RARE DARK GREEN JADITE BROOCH shops SET IN .925 SILVER Burma Made? MARKED C5

Product Name: Antique RARE DARK GREEN JADITE BROOCH shops SET IN .925 SILVER Burma Made? MARKED C5
Antique RARE DARK GREEN JADITE (Chloromelanite) FROM BURMA (now MYANMAR) SET IN .925 STERLING SILVER. Can't guarantee stone type or source, but did conduct EXHAUSTIVE INTERNET SEARCH FOR ABOVE INFO. TESTED VERY QUICKLY FOR SILVER but would still recommend visit to jeweler to confirm shops this & stone type. Is MARKED C5 in an OVAL (see photo). I searched everywhere & couldn't find what this means. Likely due to this being a VERY OLD PIECE from OVERSEAS. If anyone definitively knows what mark means, I'd greatly appreciate if you'd contact me so I can update listing. GORGEOUS STONE - HAVE TO SEE IN PERSON TO FULLY APPRECIATE. Clasp works fine, but is clearly more modern or vintage that was added at a later time (probably because the piece is SO old, the original one broke/wore out). Can easily see TARNISH IN SILVER SETTING. Silver dangles are lighter in color, though, possibly indicating they too were replaced at a later time? But is surely a VALUABLE & UNIQUE BROOCH EVEN STILL. Very EXOTIC!!.