What Is Pumice Composed of?
- Igneous rocks, including pumice, are formed when molten volcanic material cools and hardens. The National Park Service says that volcanic rock is classified according to its silicon content, with rhyolites and dacites having high levels of silicon and andecites and basalts having less silicon. Pumice forms most often from high-silicon material and generally has low iron and magnesium content as well.
- Pumice is often light in color due to its high silicon content. Being porous, it is very lightweight and will float until the open cells fill with water. The United States Geological Survey says that in the aftermath of volcanic eruption, blocks of pumice have been observed floating in the ocean.