Oval Opal Charm Pendant Necklace with Diamonds, 24kt Gold and Silver by Prehistoric Works of Istanbul, Turkey. Opal - 2.25cts, Diamonds - 0.06cts. This stunning opal is framed in 24kt gold with 6 diamonds. Looks beautiful alone or paired with other charms.  Sure to make a subtle, striking statement. Measurements, 14mm x 20mm, chain options available. The ancient Greeks believed opals gave their owners the gift of prophecy and guarded them from disease. Europeans have long considered the gem a symbol of hope, purity, and truth. Opal is considered an October birthstone. Some people think it's unlucky for anyone born in another month to wear an opal.