Lovely antique Edwardian brooch sterling silver? filigree & pale purple stone

Description

Gorgeous delicate little brooch features a large faux amethyst/purple rhinestone, open backed and bezel set into a complex filigree openwork frame.  It is likely sterling, but untested, and it has a tiny unreadable stamp on the c-clasp.  Very good condition, could use a light cleaning.  Measures just over an inch diameter.
Please look over all pictures and feel free to ask questions!