In my opninion this is EXACTLY why forgerys absolutely DESTROY the collecting market. Marbles like this are presented as antique and sell for huge dollars - and then the origin of the damn marble is called into question and no one can be sure....(the cut line is real, the white looks right, the seller is questionable, the seller is reputable, the swirl pattern is wrong, its too shiny, its NM so its been damaged on purpose, its MINT so it must be a forgery....etc etc etc blah blah blah)no one can be sure so ....
In the mean time - every marble in YOUR collection is also now questionable unless you can provide provenance.
Forgers SUCK!