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:

Akro

Yes sir.

Here is a galactic planet:

I think (by appearance) that some had a final gather in clear and other had a gather in the base color. If the latter, the light reflecting off the silver mica is filtered through that color. So the reflected light takes on that tint. A reminder to us all that all marbles are seen and perceived by reflected light. Perhaps the intent of the word is to describe whether the outer glass is clear or base color. Also, the thicker the outer layer, the dimmer the light reflected off the mica is. Or put another way - the less obvious the mica is.

Which brings me back to the question: What is a "cased" mica? All micas have an outer clear glass gather - otherwise the mica will just gradually fall off. That is part of the standard cane construction. (If someone has a vintage mica with naked mica on the outside, please speak up). What does the word mean in this context?

Perhaps its just me - but I want to know what a specific term is supposed to mean before I just accept its use only because it has become commonplace. We have a lot of words in this hobby that are casually used (and many more new words recently invented). Perhaps we should pause and ask ourselves specifically what they mean and why its use is important. Have we ever seen the term "uncased mica" used? YMMV.

All vintage micas are cane construction. All.

I'm not sure what the reference to "cased" mica means. All micas have to have a final layer of glass on the outside. A mica is a mica. The mica may be finer or more coarse, depending on how it was diced and sifted (or not). Also based on how much mica was spread on the marver and how evenly/unevenly. Like frit on an onionskin, this was a fast and fairly crude process. Outcomes vary.

I have the same - and same predicament!

Yes - Comedy and Tragedy masks in uranium glass.