What is Perlite and how does it work?

Perlite is not a trade name but a generic term for naturally occurring siliceous rock. It is a amorphous volcanic glass that has a relatively high water content (2%-6%), typically formed by the hydration of obsidian. Perlite has distinguishing features from other volcanic glasses that when it is heated to a suitable point within its softening range, it expands from four to twenty times its original volume. 

Raw perlite ore is mined in volcanic areas, crushed, and screened into different sizes before being sent to a perlite expansion furnace. The crushed ore is then brought to a temperature (1,500°F-1,700°F) where the glass softens, and the trapped water molecules turn into steam-making the small rock particle “expand” in the same manner that popcorn expands in an air popper. The result is a particle that reveals itself under a microscope as a cluster of tiny, volcanic glass bubbles-both whole and broken.   During this expansion process only the physical property changes. The chemical makeup remains the same, similar to water and ice.  

Why Perlite Works

When perlite expands clusters of minute, lightweight, insulating, glass bubbles form in its particles. These broken bubbles and surface openings on the particles provide for water and air holding capacity especially important in horticultural uses. Water is held in one of three ways: in between individual grains, in channels leading to the cores of the grains and on the highly irregular surfaces of each particle.  

Perlite and the Environment 

Perlite is a versatile mineral that is mined and processed with negligible impact on the environment. When perlite ore is expanded or “popped” by rapid, controlled heating, it expands up to 15 times its original volume and takes on a foam-like cellular appearance – essentially clusters of microscopic glass bubbles, creating a porous structure. This physical transformation makes expanded perlite an extremely effective aggregate.

Many in the green community recognize perlite-enhanced products as high-performance solutions drawn from a natural material of nearly unlimited supply throughout the world.