The occurring among the old volcanic rocks, the cavities are frequently filled with deposits of secondary minerals launched by percolating h2o. The glass by itself sorts threads, fibres, and slim partitions between the vesicles. Rhyolite and trachyte pumices are white, andesite pumices generally yellow or brown, and pumiceous basalts (for https://edenproductsltd.co.uk/2025/04/17/the-history-of-pumice-stone-from-ancient-civilisations-to-modern-day-uses/