An excerpt from a history of necklaces in Yemen Times:

In Greek mythology, Harmonia, (daughter of the Goddess Aphrodite and God of storms Ares), was gifted with a necklace made by Hephaestus on her wedding day. The necklace bestowed irresistible beauty upon the wearer. In ancient Greece, priestesses wore beaded amber necklaces because it was believed that these necklaces were the repositories of exalted energy. It is believed that Eurymachus, an Ithacan nobleman and one of the many suitors of the beautiful Penelope, had presented her a gold necklace entwined with amber.

The necklace bit in the Odyssey is in book 18 ... Pisander the son of Polyctor also gave Penelope a necklace. On who 'gifted' Harmonia, see Carlos Parada's page (scroll down to 'the wedding present').