Formed from viscous lava, perlite is a volcanic glass of rhyolitic composition that contains between 2 and 5 percent water. Most volcanic glasses contain some water, including obsidian (less than 1 percent) and pitchstone (up to 10 percent). Although the exact formation process for perlite is debated, it is theorized that the lava that formed perlite was deposited and cooled near the surface and hydrated over time. Pumice is closely related to perlite in composition but, because of the explosive way in which pumice forms, the rapidly cooling lava entrains air and becomes much less dense than perlite.
Perlite is mined by employing heavy machinery to rip or cut the material out of the earth, or by precise blasting. After extraction, the material is crushed and sized into marketable fractions. Then it goes to another plant where it is expanded, or “popped.” When heated, the water content of perlite reacts, and the perlite pops like popcorn. Perlite popping produces a lightweight product that is up to 40 times less dense than the original material.
In primary usage, perlite competes with other lightweight construction materials, like pumice, exfoliated vermiculite and expanded clay and shale. Each of these lightweight materials has its pros and cons, depending on the application, and each has retained certain niche markets. Perlite is especially favored in lightweight construction products, fillers for paints and joint compounds, horticultural soil blends and certain filtration applications. In addition to these primary markets, perlite is used for concrete aggregate, insulation, plaster aggregate and stone washing in laundries. In most offices or other locations with a “dropped” ceiling, the ceiling tiles are probably made primarily of perlite.
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