The transpiring amongst old volcanic rocks, the cavities are generally filled with deposits of secondary minerals launched by percolating drinking water. The glass alone sorts threads, fibres, and thin partitions in between the vesicles. Rhyolite and trachyte pumices are white, andesite pumices usually yellow or brown, and pumiceous basalts (like https://directmysocial.com/story4097727/everything-about-eden-pumice-stone