The occurring amongst outdated volcanic rocks, the cavities are usually full of deposits of secondary minerals introduced by percolating drinking water.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