The occurring among the outdated volcanic rocks, the cavities tend to be filled with deposits of secondary minerals launched by percolating water. The glass itself types threads, fibres, and skinny partitions amongst the vesicles. Rhyolite and trachyte pumices are white, andesite pumices normally yellow or brown, and pumiceous basalts (including https://edenproductsltd.co.uk/2025/04/17/the-history-of-pumice-stone-from-ancient-civilisations-to-modern-day-uses/