Alan

In pretty much all cases - it is undissolved (or precipitated) colorant flakes in the glass. Those flakes reflect light in most cases. A company like Peltier intentionally used it to very good advantage to cause dense colorant in the glass for specific NLRs (Golden Rebel, Zebras etc). It was more expensive for them to use excess colorant in that way, which is probably why it was done so sparingly. Marbles had to be made ultra-cheaply.

Vintage manufacturers didn't have a big barrel of "aventurine" that they chose to add rarely - or at all. Fun fact: "Aventurine" is a stone. A mineral. Quartz to be specific. There is no quartz in glass marbles.

Its not as if excess colorant in glass is a rare or valuable thing. It can appear in most glass colors when there is undissolved colorant in the glass, or in the cullet.

As noted ^ - a Bennington.

I would return it, wax intact, to the antique store. That is intentional fraud.

White is not a lifesaver color.

The blue one is a bead, not a marble. The pic is too poor to make out the others. You can buy a Mark Matthews Super Jetson. About 2.75".

Looks Pelt, but I think it would need a shove to be considered a Liberty.

Its a swirl, but the word "banded" has a different meaning long established in the collecting hobby.

It is presented in the Ravenswood ID thread. The best ones have a generous amount of transparent amber striping.

I don't think I have ever heard of a mica in Vaseline glass. Yellow - yes.

They made plenty. Example:

Red

Banded opaque.

Crud from the cullet pile. Fire brick should be white.