Given to Sabrina by her boyfriend Harvey on the eve of her sixteenth birthday, this locket is a sentimental reminder of Sabrina's ties to the mortal world.
This vintage gold locket is hard to see in stills and on-screen, despite being worn by Sabrina in almost every scene of season 1. In a behind the scenes tour of the set, Kiernan Shipka revealed that her necklace was in fact a tiny gold locket, containing two pictures of Harvey Kinkle (Ross Lynch).
I've also included the replica necklace version for a comparison to the screen accurate locket.