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