Silver,
Mother in law , was her grand mothers piece
This is a vintage late 2nd quarter of the 20th century necklace in hand set marcasite. It does not appear to be stamped sterling silver nor 925 and is likely rhodium plated. The necklace is in original box and there is also a pair of bird shaped marcasite clip earrings. They do not not match the necklace and were likely not original to the set. The estimate is based on actual recent past recorded auction sales of comparables. Retail 'asking prices' can be higher and vary.
Let me know if this is clear enough, Thank you