The happening among outdated volcanic rocks, the cavities tend to be filled with deposits of secondary minerals released by percolating drinking water. The glass by itself forms threads, fibres, and thin partitions in between the vesicles. Rhyolite and trachyte pumices are white, andesite pumices frequently yellow or brown, and pumiceous https://edenproductsltd.co.uk/2025/04/17/the-history-of-pumice-stone-from-ancient-civilisations-to-modern-day-uses/