Dacite pumice

Dacite pumiceDacite pumice
This cinder of dacite composition has so many tiny gas bubbles trapped in the rock that it floats on water. Although both pumice and scoria have an abundance of gases trapped within them; pumice will floats, whereas scoria will sink).
Shoreline deposit near Obsidian Butte area on the south shore of the Salton Sea, California.
https://gotbooks.miracosta.edu/rocks/igneous/24.html 2/2/2021