Martina | Marquise Cut Australian Opal Ring in 10k GoldMeet Martina, A Flashy Opal Solitaire Ring in Yellow Gold Bright red colors form a stripe that jumps in this classic, marquise cut white crystal opal. The opal is prong set on a diamond cut 10 karat yellow gold band that catches the light as the wearer moves their hand. A minute chip can be seen below one tip of the marquise shape when viewing the ring from a sidle angle; this was a choice made during the cutting process to maximize the stone's size,