The taking place between previous volcanic rocks, the cavities tend to be full of deposits of secondary minerals launched by percolating h2o. The glass itself sorts threads, fibres, and slender partitions in between the vesicles. Rhyolite and trachyte pumices are white, andesite pumices frequently yellow or brown, and pumiceous basalts https://edenproductsltd.co.uk/2025/04/17/the-history-of-pumice-stone-from-ancient-civilisations-to-modern-day-uses/