Post 4 you asked if Pellet sounded more clay than stone. Seeing as the chart is specific gravities clay is way at the bottom and Pellet is in the middle of other stone?
I would bet some marbles from every manufacturer will have reactivity to UV light(GLOW) There are many compounds besides Uranium Oxide that will have a UV reaction in glass. It is the bright green of Vaseline glass that we are familiar with that Uranium Oxide provides.
The first 2 pics shows this is a bead IMO. Pretty one. There may be bead boards that can ID it for you. So many billions of beads have been made it is usually tough to nail down other than a timeline.
Yes they used white Benningtons, white chinas even limestone. There are also several types of black ballot box marbles including glass, black bennington, and black on redware type clay.
If you are talking about this type, fine examples can be had for 10-50cents a piece in bulk. And fine examples of most all the jabos can be had for not much more than that. I can't see why paymuch more money for polished examples when there are plenty of nice new ones available that do not need polishing.
Hat pin toppers will usually not have a hole completely through the bead. And when the pin is missing, a remnant of the pin usually remains in the bead making a rough metal filled mark.
Actually I have found the transparent glass in slags to be clearer than what is usually found in swirls, I really don't think there is much besides experience that helps one determine whether a marble is a slag or a transparent swirl.