The transpiring between outdated volcanic rocks, the cavities usually are full of deposits of secondary minerals introduced by percolating h2o. The glass by itself forms threads, fibres, and slender partitions amongst the vesicles. Rhyolite and trachyte pumices are white, andesite pumices typically yellow or brown, and pumiceous basalts (like manifest https://edenproductsltd.co.uk/2025/04/17/the-history-of-pumice-stone-from-ancient-civilisations-to-modern-day-uses/