I have seen old/antique ornaments that are reputed to be carved from solidified lava, that are of a much more pale and grayish or buff color. It was a very fine-grained material. And not something recent.

Offhand, I don't recall reading a description of the Czech glass beads that named them "lava." I cannot say this is a mistaken idea. But I also cannot know for what period of time they may have used this descriptive identifyer either.

My point, in the reply I posted, is that these concavities are not "bubbles."

Jamey