This matched pair is cut from koroit boulder opal from Austraila.  It was hand cut in my cutting shop.  The polish is good the edges are cut for setting the stone in a bezel and the bottoms are flat. MORE BLUE FLASH THAN THE PHOTO SHOWS.

FROM THE BOULDER FIELDS OF KOROIT

SIZE:(in millimeters) 23 x 12 x 3 MM THICK EACH STONE.
WEIGHT(Carats): 20 TOTAL WEIGHT OF BOTH STONES. 
DOME: SLIGHTLY DOMED.
BOTTOM: FLAT.  
EDGE:  GOOD FOR BEZEL 
POLISH:  GOOD.