u/Sufficient_Plum_807

Hi. I'm doing a commission and a client brought me this stone to use. I haven't taken it out of the gem case since the day they gave it to me. Is this spot normal? What is it?

Doesn't affect play of fire but it looks odd. I don't remember seeing it when I first saw it or I would have said something to them. Also never seen this before on any of my opals.

Thanks in advance.

TLDR: what is this spot? Doesn't affect play of colour.