This opal is a stunner. 
I admit I'm not always drawn to opals, but this one is another level! 
The grey/black body colour of the opal and the amazing play of colour really pops. Sweeping sections of colour in a harlequin pattern makes this type of opal highly sought after, and you can see why. 
Made in the early 20th century in 15ct gold, the simple setting is all this stone needs, as it will always be the star of the show - no support act required! 
Stamped and tested as 15ct gold 
Weight approx 2.26g
Width at widest point approx 13mm
Width of shank at the back approx 2mm
Finger size M (approx US size 6.5) 
Very good antique condition. Some very light surface wear to the opal, and patina to the gold. 
No obvious evidence of treatments to the opal.