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.
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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.Its low density and porosity makes it an ideal additive for the production of certain concretes and cinder blocks. Many ancient Greek and Roman structures were built from pumice-containing materials. In addition to the construction trades, the agriculture industry has found many uses for pumice over the centuries.
Larger-sized chunks are useful for providing drainage for container plants or decorative ground covers, and pulverized powders can be used in soil mixes to provide improved aeration. In recent years, it has also proven to be an excellent soil-less medium for hydroponic gardening. And lastly, in cold weather locations, it isn’t uncommon to have various smaller-sized particles of pumice included in snow and ice traction control mixes for roads.
Interesting Facts About Pumice
In the United States, all mined pumice comes from states in the Western half of the country, including Hawaii. This is due to the presence of both active and dormant volcanoes in those states. Another large supplier of pumice to the world is Greece.
It is also worth noting that humans aren’t the only species that benefits from pumice. Most commercially available chinchilla dust bath products are made of pulverized pumice, and there are numerous accounts of marine plants taking root in chunks of pumice and marine animals living in underwater pumice deposits. It is also a common additive in cat litter.
Pumice is an extrusive igneous rock, forming as a result of the fast cooling of light-colored magmas. Its vesicular texture is a result of the depressurization of gases within its parent magma and gives it an extremely light density. Its light density and abrasive, glassy texture have led to pumice having a wide range of applications from the construction trades to agriculture, to personal care and pet care products. It can be found around active, dormant, and prehistoric volcanic sites and is valued world-wide for its extensive uses.