Brilliant Greens 26ct Natural Australian Solid Koroit Boulder Opal. 28.9mm x 15.0mm x 6.6mm thick. This natural australian solid koroit boulder opal has brilliant gem greens as its dominant color whilst the other colors include violet, turquoise and a touch of yellow. The colors flash brilliantly at certain angles. We pride ourselves in offering you boulder opal with bright gem colours.We go the extra mile to offer top quality opals in all price ranges.