Rich, It is believed by most in the collecting community that aventurine was not used on purpose in machine made marbles. Besides no need it is also too expensive and they used their own glass in making their marbles. They would not have taken the time or trouble to make aventurine glass to make marbles purposefully sparkly IMO Modern collectors think they are neat so assume it was done on purpose. This just was not the case, Even Oxblood turned out to be too troublesome and expensive to bother using. Handmades are a different story. There were many sparkly glasses used