9ct yellow gold opal october birthstone pendant necklace - 20 inches the teardrop-shaped pendant of this necklace is made from 9ct yellow gold with an opal gemstone, which makes it the perfect match for an october birthday. measuring 21mm high (including bail attachment) and 11mm wide, the pendant hangs from a chain in your choice of length. select your preference of 16, 18 or 20 inches from the dropdown menu.