A pendant is a piece of jewellery that hangs from a chain worn round the neck."a jade-green pendant on a gold chain."

As an adjective:

hanging downwards; pendent."pendant flowers on frail stems"

A locket is a small ornamental case, typically made of gold or silver, worn round a person's neck on a chain and used to hold things of sentimental value, such as a photograph or lock of hair.

A necklace is an ornamental chain or string of beads, jewels, or links worn round the neck e.g. "a diamond necklace"

An amulet is an ornament or small piece of jewellery thought to give protection against evil, danger, or disease.