Pewter Heart

The Pewter Heart is the name given to an ancient locket, which was gifted to Melinda Warren by her Warlock lover, Matthew Tate. She later trapped him inside the locket after her turned her in as a witch.

Melinda Warren and Matthew Tate
Once Melinda had figured out Matthew was a Warlock who'd copied her powers, he brought her to the townspeople, claiming that she was a witch. In revenge, Melinda created a curse, the "Warlock Curse" and cursed Matthew in the locket when he came to visit her at the town's jail. It wasn't long until Melinda was burned at the stake. According to a book that Piper read on Melinda and Matthew, the legend says that the warlock must never be freed or he will destroy the Warren line.