The Story of Pumice

Deep underground, in the fiery heart of a volcano, water mixes with molten rock...pressure building until finally finding a violent, spectacular release. The trapped water in the viscous, super-heated rock flashes to steam, blasting the magma into a frothy stone that cools, hardens, and falls to the earth as pumice…a foamed-glass stone that is hard yet friable, non-crystalline in structure, and naturally calcined—a combination of characteristics that make pumice powders and aggregates incredibly useful to a variety of industries.

The value of pumice to infrastructure and industry goes back at least 2000 years. Roman engineers knew that by adding fine-grained pumice, or “pozzolana” to their hydrated lime cement, the result was a strong, durable concrete. Some two millennia later, much of their empire of concrete—roads, aqueducts, temples, stadiums, piers—still stands defiantly against the ravages of time. Today, pumice powder is still being used as a superior pozzolan to super-charge concrete strength and durability, but is also used widely in a variety of industrial processes and product applications.

The Hess Pumice Deposit

In the southeast corner of the State of Idaho, 23 miles northwest of Malad City, lies a vast reserve of white, pure pumice that is in demand all over the world. That demand is the result of two factors: the quality and brightness of the pumice, and the company that mines and refines it: Hess Pumice.

The pumice deposit is located on the shoreline of an ancient lake known as Lake Bonneville...a vast, freshwater lake that once covered much of North America’s Great Basin region (most of Utah and parts of Idaho and Nevada). The Great Salt Lake is all that remains of Lake Bonneville.

The volcano that produced the pumice is about a mile to the north of the mine. The volcanic ash (pumice) was deposited in the lake, where it was washed and stratified. This process cleaned the pumice of the undesirable heavy minerals that are often found in other pumice deposits.

Hess Pumice Mine USA The Hess Pumice Wright Creek Area pumice mine in Southeast Idaho, USA

In 1958, a local farmer, frustrated by his inability to grow anything in the thin soil over what is now the Wright’s Creek Area pumice mine, leased the ground to Marion Hess, who ripped up the white volcanic rock and sold the crushed pumice to a building block manufacturer in Salt Lake City. From those humble beginnings, the now carefully refined, pure and white pumice from the Hess mine is in demand by industry worldwide.

Pumice Mining and Processing

Mining pumice is, environmentally, a low-impact process. Most pumice is surface-mined. The soil (overburden) covering the pumice is pushed aside and stockpiled for later reclamation of the mining site. The pumice is ripped or scraped loose and pushed to the crusher for preliminary processing (mine grades). The pumice is then loaded and trucked to the plant for additional processing.

That pumice is then typically dried to the necessary moisture content ideal for refining, then lifted into the plant to run down through the crushers, shakers and screens, separated by grade, purified, and finally packaged or bulk loaded for delivery.

Mohs Hardness Scale

Material Mohs Hardness  
Talc 1 On the Mohs Hardness Scale, Talc is the softest, Diamond the hardest.
Feldspar 6
Pumice (Hess Deposit) 6
Quartz 7
Diamond 10  

Chemical Makeup of Pumice

Pumice is not created equally—it varies greatly in its chemical properties (and usefulness) from deposit to deposit, but essentially, pumice is primarily Silicon Dioxide (Amorphous Aluminum Silicate), some Aluminum Oxide, and trace amounts of other oxides. [MORE]


•If you’d like to run tests and trials using our pumice in your commercial product formulation or industrial process, please contact us at with your request. We look forward to answering your questions, helping you select the best grade for your process, or helping you explore the fit of pumice for your needs. PLEASE include your name, your company or organization, pertinent project details, ship-to address, and preferred contact information in the sample request email.

pumice store logo

•If you’d like a bit of pumice for personal use, we have a nice selection of pumice grades available to purchase via our Pumice Products Store.


We know pumice. Perhaps you are exploring the possibilities—thinking pumice may fit your particular need. We invite you to contact Brian Jeppsen, VP Research and Development, at (208) 766-4777 x111 or email:

Pumice is a frothy amorphous glass made up of a maze of air-filled vesicles.

3 generations of Hess Born of earth and fire, pumice is a natural, sustainable volcanic glass with amazingly versatile properties widely utilized by industry. Anciently, the Romans and Greeks also used pumice.


refined pumice powder Refined pumice powder from the Hess pumice mine in Southeast Idaho. pumice vesicles Magnified image of pumice vesicles, formed by the expansion of trapped gases when molten lava rapidly cools. pumice nugget stone A typical pumice stone, it’s frothy structure clearly visible. About Pumice Website Learn more about pumice at the website. 208.766-4777  •  Malad City, Idaho 83252