The happening between old volcanic rocks, the cavities are often stuffed with deposits of secondary minerals released by percolating water. The glass alone varieties threads, fibres, and skinny partitions amongst the vesicles. Rhyolite and trachyte pumices are white, andesite pumices frequently yellow or brown, and pumiceous basalts (including come about https://edenproductsltd.co.uk/2025/04/17/the-history-of-pumice-stone-from-ancient-civilisations-to-modern-day-uses/