The occurring among the previous volcanic rocks, the cavities usually are crammed with deposits of secondary minerals released by percolating water. The glass alone types threads, fibres, and slim partitions involving the vesicles. Rhyolite and trachyte pumices are white, andesite pumices frequently yellow or brown, and pumiceous basalts (like occur https://edenproductsltd.co.uk/2025/04/17/the-history-of-pumice-stone-from-ancient-civilisations-to-modern-day-uses/