Pretty wild. I've seen pictures similar to the opaque blue on white before but I believe the marble was a lot bigger that the ones you show here. Even the large ones I'm not 100% convinced on their origins (not that I need to be, more a curiosity thing). What's the actual size of these?
From the pics I'd guess glass marbles but more pics or seeing in hand might narrow it down a bit more. There are newer marbles that can look similar but I think these are older, just not sure how old. (lot's of help I know)
Nice examples either way.