The term can be used synonymously with "volcanic ash." It is actually mined from volcanic ash deposits, or it could be made by crushing rock pumice. “It’s really essential to always thoroughly clean it just after every single use since microbes can improve over the surface of your stone,” suggests https://edenproductsltd.co.uk/2025/04/17/the-history-of-pumice-stone-from-ancient-civilisations-to-modern-day-uses/