The material cools so immediately that atoms within the melt are not able to organize them selves right into a crystalline composition. Thus, pumice is really an amorphous volcanic glass known as a "mineraloid." The key with pumice stones is to only rely on them on resilient surfaces like porcelain https://edenproductsltd.co.uk/2025/04/17/the-history-of-pumice-stone-from-ancient-civilisations-to-modern-day-uses/