The happening among previous volcanic rocks, the cavities are frequently stuffed with deposits of secondary minerals released by percolating water. The glass alone forms threads, fibres, and slender partitions among the vesicles. Rhyolite and trachyte pumices are white, andesite pumices frequently yellow or brown, and pumiceous basalts (such as happen https://edenproductsltd.co.uk/2025/04/17/the-history-of-pumice-stone-from-ancient-civilisations-to-modern-day-uses/