Again, I take issue with calling this "pumice-" I'd prefer "pumiceous obsidian," but in this setting, it's a pretty trivial concern. Unlike pumice, it's quite dense. Also unlike pumice, it's quite tough. Most "real" pumice is weak enough to pull apart or crush with one's bare hands; this sample would turn them to handburger. Still, the commonalities are more important than the differences: rhyolitic, vitreous, and very, very foamy. Also like true pumice (in many/most cases) there is a distinct fabric: the threads of glass tend to be oriented horizontally in this view. Likewise, the long axes of the vesicles are dominantly horizontal. I presume this reflects the strain/flow regime as this block finally "set" and cooled into solid form.
This is not the same block as yesterday's example, but a bit farther along the path. Lens cap is 52 mm in diameter.