The taking place between old volcanic rocks, the cavities are usually crammed with deposits of secondary minerals introduced by percolating h2o. The glass itself sorts threads, fibres, and slim partitions amongst the vesicles. Rhyolite and trachyte pumices are white, andesite pumices frequently yellow or brown, and pumiceous basalts (for example https://funbookmarking.com/story19402736/5-simple-techniques-for-pumice-stone