Boulder Opal Ceylon Sapphire Yellow Gold Necklace Necklace measures approximately 1.75 " pendant length including bail. What is this unique marbled gemstone? It is a special formation sourced from ironstone boulders beneath the ground. They are set apart by a layer of solid brown ironstone left on the back side of the stone slab. Areas of colorful opal form in cracks and fissures in these boulders. We paired with this pendant a 0.22ct Ceylon Sapphire, setting it all in 14K yellow gold.