Tale as old as Time Opal necklaceThis genuine opal necklace comes with 14k plated gold and a 16" adjustable to 18" chain. Precious opal is a rare gemstone that's more rare than diamonds. This is because the natural processes that create opals rarely occur. Opals are formed when water seeps through sandstone, picking up silica particles, and then flows into cracks and voids in sedimentary rocks and volcanic areas. It takes over two million years for this solution to harden into opal