The opal you describe should be @ or about $100 per ct.
John, as a former dealer of Mexican opal I can assure you that
anyone who knows this material will tell you , sight unseen, your
opal cannot be appraised by description alone. It must be seen in
person by a qualified pro. And many of those pro’s, for better or
for worse, might be unwilling to disclose its true value to you.
Unlike diamonds with their 4-C’s, Opal grading and appraisal
comes from looking at hundreds of thousands of stones- i.e. mucho
experience. I remember one time in Tucson; after grading about
twenty thousand stones one day, I walked back to my hotel
exhausted ( due mostly to the fact that one of my partners was an
incessant talker - the kind that repeats the same stories over
again.), and became aware of a very curious sensation. My sense
of colors was profoundly heightened. Traffic lights became
subjects of awe. Quite a nice experience I must say. A buyer(of
Gemstones) friend of mine, who is mostly color blind, tells me
his color awareness has increased since he started buying stones.
Yeah, I know, it’s strange. But stranger things do happen. To
come back to your opal John, the best advice I can give, other
than showing it to a trusted pro, is to find a similar opal for
sale and draw your comparison there.
Best of luck, Peter Slone