The happening among old volcanic rocks, the cavities are frequently full of deposits of secondary minerals released by percolating h2o. The glass by itself kinds threads, fibres, and skinny partitions in between the vesicles. Rhyolite and trachyte pumices are white, andesite pumices usually 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/