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Pumice: Definition, Uses & Facts

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  • 0:00 What Is Pumice?
  • 1:55 Uses for Pumice
  • 3:18 Interesting Facts About Pumice
  • 3:55 Lesson Summary
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Lesson Transcript
Instructor: Heather Pier

Heather has taught high school and college science courses, and has a master's degree in geography-climatology.

Learn about pumice, an extrusive volcanic igneous rock with a unique vesicular texture and a wide variety of uses, from beauty products to construction materials. After you have watched the video, test yourself with the quiz questions.

What Is Pumice?

When you see the word pumice, the first thing that probably comes to mind are those stones you rub on your feet to remove calluses. While that is not an entirely incorrect assumption, there is much more to pumice than pedicures.

Pumice is an extrusive igneous rock formed as a result of volcanic eruptions. Extrusive means that it forms outside of the volcano (as opposed to inside the volcano in the magma chamber), and as a result, the magma cools quickly after exiting the volcano. In many cases, pumice-bearing magmas tend to erupt explosively, leading to rapid cooling. This quick cooling gives pumice its characteristic vesicular texture. Vesicular textured rocks appear to have thousands of tiny and microscopic, Swiss cheese-like holes in them and, consequently, feel very light for their size because of the lack of density in the rock matrix. It is one of the few rocks that has a low enough density to be able to float on water (at least until its pores become filled). The vesicular nature of pumice is a result of both fast cooling as well as the gases in the parent magma becoming depressurized and giving off some of its gases upon exiting the volcano.

Pumice will occasionally contain visible crystals that resemble tiny shards of glass. Because pumice typically forms from light colored magmas, such as silicic or felsic, it too tends to be light colored, with shades of white, grey, and pale green being the most common. If you encounter a rock sample that appears to be pumice based on its texture and overall appearance but does not float in water and/or is of a darker color composition, it is most likely pumice's close relative, scoria. Scoria forms in much the same way as pumice, but is formed from darker, denser magmas.

Uses for Pumice

So, it's time to address the pedicure assumption. Yes, polished chunks of naturally occurring pumice can be used to remove calluses and buff rough patches of skin, as well as remove hard water toilet bowl rings. The rough, glassy texture of pumice makes it an excellent abrasive, and has a wide range of abrasive uses, including skin exfoliating products (both pumice stones and liquid exfoliants), eraser materials, Lava-brand soap, creating 'stone washed' jeans, dental polishes and toothpastes, and industrial polishes.

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