Pumice: Technical Data

the amazingly versatile pumice stone

Pumice from the Hess Pumice desposit in Southeast Idaho USA is an amazingly versatile stone, used in a wide variety of products and industrial processes.

A micrograph of a tiny grade #2 pumice stone, showing the friable nature of pumiceā€”ie. it holds its foamed-stone nature even when crushed to fine particles.

Sourced from the world's purest commercial deposit of white pumice

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BORN OF EARTH AND FIRE, pumice is formed during volcanic pyroclasic events, typically spewed as ash that falls and drifts into deposits or as part of a massive pyroclastic flow. Many factors affect the useful quality, color, and purity of a pumice deposit, but on a chemical analysis level, pumice is basically an aluminum silicate. With no crystalline structure, pumice is a naturally calcined amorphous glass made up of a maze of air-filled vesicles.

The word pumice is derived from the Latin word pumex, meaning foam. Deep underground, molten rock incorporates water and other gases, and when the magma erupts from a volcanic vent, the gases flash off, leaving behind a frothy, vesicle-riven structure that quickly cools, solidifying the foamy structure.

Pumice enjoys a well-deserved green cred, as it is an abundant and sustainable resource, easily mined from surface deposits, and, having been naturally calcined (super-heated) in the fiery heat of a volcano, the only refining needed is to crush and screen it to grade.


Description: Non-crystalline (amorphous) foamed glass stone of volcanic origin. Grey-white (stone grades) to white (powder grades) in appearance.

Brightness (GE): 84

Hardness (MOHS): 6

pH: 7.2 (neutral)

Reactivity: Inert (except in the presence of calcium hydroxide or hydrofluoric acid)

Loose Bulk Density: Varies with grade (Download Technical Data Sheet of specific product below)

Specific Gravity: 2.35

Softening Point: 900 Degrees C

Water Soluble Substances: 0.15%

Radioactivity: None


Chemical Name: Amorphous Aluminum Silicate

Composition: Primarily made up of Silicon Dioxide and Aluminum Oxide with traces of other oxides.

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%

Crystalline SiO2:: none detected


Pumice Safety Data Sheet (PDF)


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Sourced from the world's purest commercial deposit of white pumice

hess pumice logo