Perfect condition, seems to have never been used. I've got to guess Victorian to Edwardian era because the gold is marked on the backside (see photos). A real beauty, awaiting your own insert - a tiny photo, a lock of baby's first hair trim, sand from the beach where you got married - you can be creative and really make this one your own. The locket part lifts up (a light pry with a pocket knife blade). Full measurements are noted on the photos.
Very good to excellent condition for age and type, it would be between 130-180 years old but just elegant. I always love seed pearls and these are nicely matched for size. I see nothing to report as a flaw. Cover glass is there.