Very hard to tell from pics, but it looks like it might be. I'm not used to the color of a mist marble being described as strands. It's usually more like a thin wash of color. In hand, does it look like the interior glass (not counting a core) is colorless, and the blue is more-or-less like a "veil" of color just on the exterior?
If not, it wouldn't be a "mist." At least as I understand it. It's also far darker than mists that I've seen.
I don't know of any cased mist marbles but that's not saying much, since it's not a type I collected when I was in my Old German frenzy. Mainly because I never ran across one, I admit. Some of them have mica added, which is what I was really looking for.
If the color is really strands, maybe it's a banded transparent. They're sometimes cased. In one of the last pics, it looks like the blue is "shrunken."
Very strange. But what a nice "jelly" type blue.
Maybe some of the "antiques only" people will know better, if we can root them out . . .
Dan, what do you think?