The taking place among the previous volcanic rocks, the cavities tend to be stuffed with deposits of secondary minerals launched by percolating h2o. The glass itself forms threads, fibres, and skinny partitions between the vesicles. Rhyolite and trachyte pumices are white, andesite pumices typically 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/