About Our Pumice

Pumice is abundant and found world-wide, but all pumice is not the same—nor are the companies that mine and refine it.

Pumice is Not Just Pumice

Pumice deposits are found world-wide, but the pumice in commercial deposits can vary significantly in key performance characteristics. Pumice is not just pumice. Purity matters. Density and hardness matter, as does the particular chemical composition. And for some applications, color matters too. For example, pumice is an excellent abrasive for sensitive applications such as polishing television glass and preparing circuit boards—and our growth into an international pumice supplier was fueled by the fact that our pumice provided superior abrasion performance and natural purity over pumice available (to some customers) nearby.

Our exceptional pumice deposit is the result of an ancient volcano that dropped volcanic ash onto the surface of vast inland paleolake—known as Lake Bonneville (which once covered much of present-day Utah and extended into Idaho and Nevada)—where it was washed via years of relentless wave action, freeing heavy impurities to fall to the bottom and piling the purified pumice in a deep deposit against the northern shore.

Pumice: So Much More than a Lightweight Aggregate

pumice stockpile mine grade 3/8-fines HP Grade 1/2: magnified and actual size

TOP: Pumice stockpile (Hess Pumice Grade 3/8 fines MN), slightly damp from a recent rain. ABOVE: Hess Pumice Grade #1/2, magnified x50 on left, actual size on right. The micrograph shows the friablity of pumice, retaining its foamed-stone form factor even crushed to tiny granules.

Physically, pumice is a naturally calcined volcanic glass foam consisting of highly vesicular strands permeated with tiny holes. Per the USGS (2011), just about half the pumice mined in the US (49%) goes into making common building blocks. Then landscaping applications (33%) and as a lightweight aggregate in concrete (8%). For most of such uses, any pumice will do. But a few select pumice deposits have the purity, physical characteristics and chemical makeup to be extremely versatile and valuable in a variety of industrial and agricultural processes. The Hess deposit in southeast Idaho is one of them.

The Agricultural Frontier

Agricultural applications for pumice present intriguing possibilities. Currently, pumice utilization within the wide variety of agricultural processes is poorly understood, yet the fit of pumice into a number of performance-enhancing ag processes is promising, especially as a soil amendment and in waste management. The best reference points for the applications best enhanced by pumice are in the current use of pumice-like products: expanded perlite and vermiculite; expanded shales and clays. Because these expanded products use an energy-intensive superheating process to transform them into a light, frothy state, they are not economically viable for typical scale of agriculture applications. In high-yield agricultural applications—green houses, roof and urban gardens, high-traffic turf fields, high-value crops, biofiltration constructs—the cost of engineered, amended-soil components can be significant. Pumice functions beautifully in these applications, and the larger the scale of the project, the more pumice becomes the ideal way to go.

THE ECONOMIC CASE FOR PUMICE. Pumice is volcanically-expanded (calcined) and so needs no superheating to reach its physical state of wide application and valuable usefulness. Plus, the grades most useful for the broad ag industry are overwhelmingly mine grades, which do not need the additional drying and refining necessary for the specialized pumice grades used as abrasives, concrete pozzolans, exfoliants, and functional fillers/extenders for plastics, rubber compounds, paints, and industrial coatings.

Mine grades are available by the ton, loaded into trucks or rail cars. Mine grades are also available packaged in palleted supersacks to meet operational and storage needs.

The Technical Data

Chemically and structurally, pumice is an amorphous (no crystalline structure) aluminum silicate made primarily of Silicon Dioxide (76.2%), Aluminum Oxide (13.5%) and less than 2% of several other oxides. Pumice has a long in-soil lifespan, providing the needed structure to improve poor native soils indefinitely. Pumice is absorbent, but does not get soggy. Pumice is hard, yet friable, retaining its foamed stone form factor even when crushed to fine grades.

Chemical Name: Amorphous Aluminum Silicate
Hardness (MOHS): 6
pH: 7.2
Radioactivity: None
Loss on Ignition (LOI): 5%
Softening Point: 900 Degrees C
Water Soluble Substances: 0.15%
Acid Soluble Substances: 2.9%
Reactivity: Inert (except in the presence of calcium hydroxide or hydrofluoric acid)
Appearance: White Powder
Whiteness GE Brightness of 84
Silicon Dioxide: 76.2%
Aluminum Oxide: 13.5%
Ferric Oxide: 1.1%
Ferrous Oxide: 0.1%
Sodium Oxide: 1.6%
Potassium Oxide: 1.8%
Calcium Oxide: 0.8%
Titanium Oxide: 0.2%
Magnesium Oxide: 0.05%
Water: <1.0%
Crystalline Si02: None Detected

Put Pumice to the Test

We publish a lot of data about our pumice, including chemical and physical data and a sieve analysis for each grade, but ultimately it comes down to the giving it a try and quantifying the results. Want to talk to a pumice expert? Give us a call. We’re happy to work through it with you—we have a lot of experience working with innovative companies and individuals looking to develop new processes and pioneer applications that include pumice. Let’s discuss the possibilities.

Hess pumice production complex

The Wright Creek Hess Pumice Mine in Southeast Idaho has confirmed source yield in the millions of tons. Minimally-processed mine grades are available by the ton and loaded for truck shipment at the mine.

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