The phrase can be employed synonymously with "volcanic ash." It is mined from volcanic ash deposits, or it can be produced by crushing rock pumice. “They come in lots of sizes and styles and also have various residence uses, from overall body treatment to scrubbing grease off a stove.” Pumice https://edenproductsltd.co.uk/2025/04/17/the-history-of-pumice-stone-from-ancient-civilisations-to-modern-day-uses/