The happening amid previous volcanic rocks, the cavities are frequently full of deposits of secondary minerals introduced by percolating h2o. The glass itself sorts threads, fibres, and slim partitions among the vesicles. Rhyolite and trachyte pumices are white, andesite pumices typically yellow or brown, and pumiceous basalts (including happen in https://edenproductsltd.co.uk/2025/04/17/the-history-of-pumice-stone-from-ancient-civilisations-to-modern-day-uses/