40 years, I love it—well, I have been around awhile too and I have never seen one like this one.
I respect Randy’s opinion for sure. If you trust him, send it to him for a proper ID.
This one even includes some Akro Oxblood imho--a very cool marble even in the normal size.
It would be more believable if it were measured @ 9/16”. There is always a measure of “ones that were missed” by quality control.
These smaller ones never act the same as the larger ones.
Generally when you find a "Sparkler" this small, it has been re-worked or polished--a bummer from my perspective.
Yours has obviously not been re-worked.
You keep this one apart and if you ever get to a Marble—Show—take it along for an ID.
Nice marble—I will stick with Akro—a “Sparkler.
This is my best----
Marble—On!!