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