What Is Perlite Composed Of?

Perlite is made from the expansion of hydrated obsidian.

Perlite is a form of obsidian (lava glass) that has a high water content. Upon heating to approximately 900 degrees C the water releases, leaving a very light, highly porous and commercially valuable product that has expanded up to 20 times its original volume. Although initially perlite's color is light gray to glossy black, after processing it is totally white. Perlite is very light and gritty to the touch.

Composition

Perlite is composed chemically of a mixture of oxides including silicon (72 percent to 75 percent), aluminum (11 percent to 14 percent), sodium (2.8 percent to 4.3 percent), potassium (4.8 percent to 5.7 percent), iron (0.5 percent to 0.9 percent), magnesium (0.10 percent to 0.25 percent) and calcium (0.1 percent to 0.3 percent).

Production

As far as it can be deduced, Greece and the United States are the world leaders in perlite production. When perlite is heated, its internal moisture causes it to "pop" like popcorn. The final white color is due to an abundance of bubbles produced by the popping or expansion.

Applications

Perlite finds a broad spectrum of applications, including in soil mixes, as a filter aid, in hydroponics, in plaster, in ceiling tile, in insulation and in certain concrete formulations. It is useful as an insulating material because of its internal air spaces.

Substitution in Soil Mixtures

Polystyrene foam is used as a substitute in some soil mixtures, but a comparison reveals that perlite has far superior water retention. Although perlite is lightweight, polystyrene is excessively lightweight, which can cause it to rise to the top of the soil mixture.

Safety

OSHA considers perlite dust to be merely a nuisance dust, presenting no out-of-the-ordinary safety issues. It contains very little quartz content, and is not associated with asbestos. Of course normal precautionary measures should be taken, such as avoiding getting perlite in the eyes or ingesting it.

References

• The Perlite Institute
• United States Geological Survey
• Nor-Cal Perlite Company

Resources

• OSHA; "Perlite (Total Dust)"
• Dicalite Europe; "Perlite"