Perlite: Handle with care


Perlite is a generic name for naturally occurring siliceous rock. To be more precise Perlite, also known as “Sponge rock”, is an amorphous volcanic glass with a relatively high water content, formed by the hydration of obsidian. It occurs naturally and has the unusual property of greatly expanding when heated sufficiently.

The Chemical composition of perlite is: SiO2 70%; Al2O3 15%; Na2O 4%; K2O 4%; FeO 1%; MgO 0.5%; CaO 1% and water H2O 4%. (very simplified analysis).

Perlite, when quickly heated at temperatures of 860–890°C, softens (being glass). The water that is trapped in the structure vaporizes and escapes. This causes the expansion of the material up to 15 times its original volume and the expanded perlite bulk density can be up to 150 kg/m³. Because of its numerous properties, Perlite has many commercial applications, including its use in horticulture.

In horticulture, perlite is being used, as a component, in various potting mixes. A perlite containing mix is open to air (perlite provides aeration) and has good moisture retention properties for better plant growth. Perlite's usefulness is due to the fact that being a form of natural glass is chemically inert, has a pH of about 7, is also soft, absorbent, sterile and weed free.

It has similar properties and uses to vermiculite but generally provides better air filled porosity and less water. Perlite, if not contained, it will float.

Primarily Perlite is mixed with moss, pine bark, coconut by-products, soil and expanded clay.

Unfortunately, it is these advantages of perlite that makes it “hazardous”.

Perlite is very light, very porous, has a very large surface area and breaks and pulverizes easily.

Perlite dust can be extremely fine and being light, it remains airborne for much longer periods of time than normal dust. Because it can be inhaled easily, it is very dangerous. Inhaling perlite dust is no different to inhaling smoke, cement dust, or any other dangerous dust. It goes straight into your lungs and coughing is the first reaction. Although it hasn't been proven yet that it is Carcinogenic,it can cause problems. A breathing mask should always be used when handling dry, dusty materials, for example emptying a plastic bag into a container. It is wise to keep perlite moist all the time.

Eyes are also vulnerable. Protect your eyes. Remember, Perlite is like glass. If dust affects your eyes, wash them with plenty of water and if pain persists visit your Doctor to remove any larger grains present. Do not take risks.

Pumice is a natural, Perlite like product. Perlite is cheaper, much easier to obtain and comes in assorted sizes.