The happening among the previous volcanic rocks, the cavities are usually full of deposits of secondary minerals launched by percolating water. The glass alone sorts threads, fibres, and thin partitions concerning the vesicles. Rhyolite and trachyte pumices are white, andesite pumices usually yellow or brown, and pumiceous basalts (for instance https://bookmarkport.com/story21823373/facts-about-pumice-stone-revealed