Expanded perlite is a mineral constituent of horticulture soils and is derived from naturally hydrated obsidian – a volcanic glass.

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 (around 1500 degrees 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.

The mineral is otherwise unchanged in composition and is added to organic components like peat moss to aerate and proved drainage for resultant soils.