Belk & Co. Opal And Diamond Pendant In Sterling Silver. This sterling silver pendant necklace features 0.70 ct. t.w. opal, and 0.025 ct. t.w. diamond that measures 14.0-mm. length x 8.38-mm. width, and hangs on an 18-in. length chain. Almost all gemstones have been treated to enhance their color and require special care.