Alan

Swirl, not a cork.

Just a purple machine made clearie with a cold roll.

To the OP's question: These days - new collectors want "stuff" in their marbles. They want what they think is premium....what they think other people want/don't have. And thus having "stuff" in their marble is desired. So called "aventurine". "Lutz". "Mica". etc etc. It has become "What the cool kids have". There is little rhyme or reason to it beyond catchy words. People chasing oxblood are so eager for it that many things red, brown or dark red are frequently mistaken for "oxblood". Eager for it, people see things through that hopeful filter.

This is correct.

Consider the possibility (however small) that it may not be clay. In the pics (which may be different than in-hand) the graining seems exceptionally dense and fine - and therefore hard. I think there is a possibility that it could be porcelain.

"Mint +" That is the sound of tap dancing. WTH is "Mint +" ????

I love photos like these where the prospective buyer has no ability to determine their condition.

That's interesting, because I don't care if it has any UV reaction at all. (Its not as if UV is a determinate of age, value, collectability/rarity or manufacturer). Backlit photos on the web almost universally take the prize for the worst photos available. Focus, exposure and the ability to ID it backlit is usually miserable.

Dug Akro.

It looks like Akro glass. Possibly a wonky flop-over cork (you can see the fold line).

If it were me: I would pass on this cats-and-dogs mixture. Take that money to a marble show and buy ONE marble well-priced at that amount.

A Red planet: Possibly inhabited?

Agree, not a Popeye.

It could be anything...some scrap. UV reaction is not a big thing.

A galaxy full of stars: