Lancastrian Jewellers has dated this piece to the 1960s.
The necklace also has a full set of hallmarks on the back of the head indicating it was imported and assayed in London in 1965.

We do also have the matching bracelet for sale, please send us a message if you are interested in the set.
Matching Bracelet - https://www.etsy.com/uk/listing/1574449257/vintage-marcasite-snake-serpent-sterling?ref=listings_manager_grid

STONES
Marcasite and Green Paste eyes
METAL
Sterling Silver
MEASUREMENTS
Measures 16" approx in length
Link measure 3.5mm across
Snake head 9mm wide
Tail across widest part 4mm
WEIGHT
27 grams
HALLMARKS
925 on the fastener

Import Mark, 925, Date letter k (1965)
CONDITION
This stunning silver Snake collar necklace remains in excellent Vintage condition. The stones are all secure and the fastener shuts firmly with an added safety catch for peace of mind. The snake boasts crisp and clear hallmarks to the back of the head. The links remain free from any marks and damage. A beautiful necklace that would make a lovely gift or a unique addition to anyones collection.
Lancastrian Jewellers has dated this piece to the 1960s.
We are a third generation jewellers in the north of england, UK. Specialising in quality antique, vintage and fine jewellery
You can view the stock and full dealer information on the Lancastrian Jewellers Profile Page