The taking place amid old volcanic rocks, the cavities tend to be filled with deposits of secondary minerals launched by percolating h2o. The glass alone forms threads, fibres, and thin partitions amongst the vesicles. Rhyolite and trachyte pumices are white, andesite pumices frequently 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/