GroveKeeper
Shohin
Pumice is generally less dense than water, scoria generally more. Scoria is generally dark in color and has more iron and magnesium than pumice - it typically comes from a different type of volcano than pumice does. Both are volcanic glass with air bubbles in them, but the definitions are not very precise. There is dark pumice and light scoria.
Maybe scoria was the wrong word. What I mean to say is, maybe when a volcano is spewing out hot rock, some of if may not have as many air bubbles as the rest, right? But it falls into roughly the same place as everything else. When we mine it, the rock is labelled pumice but there isn't going to be a homogeneous distribution of air bubblea throughout the entire layer of pumice?
I'm not a geologist so I'm going off of intuition.