I’m thinking of getting this ring. It’s antique 14K gold with a natural stone and it’s hard to see in pic but half of it is a darker gray with black inclusions at the bottom then the other half is a purple iridescent bluish color with like shimmer with flecks of iridescence…but the darker grayish part made me think it is labradorite or possibly rainbow moonstone or some other type of moonstone…I can’t tell 
It could be anything! I do see as why you thought it could be opal. A hardness tester won’t help all three are in the 6-6.5 range. Have the jeweler ask another expert or spend the money and have it tested if you really want it.
Good luck & God Bless,
Bob
As previously stated, testing would be required to conclusively answer. Looks like maybe white laboradite or opal.
It looks like an opal doublet. Something does not quite look right or the picture is just not all that clear. It’s hard to tell. If you do purchase the ring, I hope you have the option of returning it if not satisfied.
All the best with your purchase.
Otter.
looks like opal to me, although can not confirm authenticity and if it is synthetic without testing.
It looks like opal but isn’t a large enough image to guess further. Is the back open or closed? Can you see through it? Might help in identification. Not, of course, that any sure ID is possible from a photo.
