To be a double ingot that crease (or evidence of it) should go all the way around the marble. And this one looks more like a game marble to me. Flinties will have an opalescent glow when backlit and many will display "fish eyes" at the poles. I think Akro may have packaged them as Fire Opals too.
Sure is a pretty thing. It doesn't look American made to me. It may be an English Whispler but at over 1 3/4" I sort of doubt it. At that size, Vacor seems like a possibility but I have not seen one like it.
A few? That's the only one I have ever seen. lol
Nobody has ever dug Master, as far as I know, and that probably at least partially explains the lack of errors you see.