The taking place amongst outdated volcanic rocks, the cavities are frequently full of deposits of secondary minerals introduced by percolating h2o. The glass alone kinds threads, fibres, and skinny partitions among the vesicles. Rhyolite and trachyte pumices are white, andesite pumices frequently yellow or brown, and pumiceous basalts (such as https://edenproductsltd.co.uk/2025/04/17/the-history-of-pumice-stone-from-ancient-civilisations-to-modern-day-uses/