Pendant is 62 x 11mm, including top loop.
It's marked '925' to the back for sterling silver 925 grade.
Probably British and from within last 30 years.
The snake chain necklace is not original to the piece.
It's 15" with a lobster clasp closure (so it sits high in the neckline).
It's 925 silver and marked 'Italy'.
Weighs 9 grams total.
Very good condition.
See pics.