The developing amid old volcanic rocks, the cavities are usually stuffed with deposits of secondary minerals introduced by percolating h2o. The glass by itself sorts threads, fibres, and skinny partitions concerning the vesicles. Rhyolite and trachyte pumices are white, andesite pumices frequently yellow or brown, and pumiceous basalts (such as https://edenproductsltd.co.uk/2025/04/17/the-history-of-pumice-stone-from-ancient-civilisations-to-modern-day-uses/