Mid-Century Australian Black Opal & Diamond Ring in PlatinumMid Century Australian Black Opal Diamond Ring in Platinum. This electric Mid Century cocktail ring features a 1. 68 carat Lightning Ridge black opal and . 67 carats of diamonds finished in platinum. The Australian black opal features iridescent shades of fiery red, neon green, and night sky blue. The opal is prong set and haloed by fourteen (14) . 04 carat accent diamonds. Two (2) . 058 carat baguette diamonds are mounted on the shoulders of the