Pumice /ˈpʌmᵻs/, called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals. It is typically light colored.
Pumice is a frothy amorphous glass made up of a maze of air-filled vesicles.
PUMICE IS BORN in 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.
It begins deep underground, in the fiery heart of a volcano, water mixing 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.
Pumice made its mark in history as being of value to industry when Roman engineers combined pumice aggregate and fine-grained pumice (a pozzolan) with their hydrated lime cement to make a lightweight, enduring concrete. Today, pumice is still being used as a superior pozzolan to super-charge concrete, but is also used widely in a variety of industrial process and product applications.
Pumice enjoys a well-deserved green credibility, as it is an abundant and sustainable resource, easily mined from surface deposits, and by virtue of being naturally calcined in the fiery heat of a volcano, the only refining needed is to crush it to grade.
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.