Perlite is a type of volcanic glass that expands and becomes porous when it is heated. When heated, it can expand to as much as twenty times its original volume. This expansion is the result of heated water: when the glassy lava rock is heated to 1,600 degrees Fahrenheit (871 degrees Celsius), the water molecules trapped in the rock turn into vapor which causes the rock to expand. (This is the same principle as the water in pop corn that causes the kernel to pop when it is heated.) Before it is expanded, perlite is commonly gray, but can also be green, brown, blue or red. After it has been heated, perlite is typically light gray to white.
Volcanic glass forms when molten rock (lava) pours out of a volcano and cools very, very quickly. Because is cools so quickly, there is no time for crystals to form or for water to escape. Instead, the lava hardens immediately into this glass-like material containing 2-5% water. It is a silicate rock, which means that it has a high percentage of silica (Si).
Perlite is known in industry in two forms. Crude perlite is prepared by the crushing and screening of perlite into various size fractions. Expanded perlite is perlite after it has been heated.
The name perlite (also spelled pearlite) comes from the French word perle which means pearl, in reference to the “pearly” luster of classic perlite.
Unfortunately there is limited information about perlite production and consumption in the world. However, it is still accurate to say that the United States is one of the world’s largest producers and consumers of crude perlite and expanded perlite. A number of western states including Utah and Oregon produce perlite, with New Mexico being the most important perlite-producing state.
The United States, however, is not the only significant producer of perlite. Other countries that are believed to produce large amounts of crude and expanded perlite include China, Greece, Italy, Philippines, Mexico, and Turkey. Even though the United States has large resources of perlite, most is still imported, with nearly all of it being imported from Greece.
Perlite is used in a number of different situations. The majority of perlite is used in construction products, mainly ceiling tiles and roof insulation products, but also as refractory bricks (a refractory brick is a brick designed to withstand very high temperatures), pipe insulation, and filling in masonry block construction. For example, loose perlite is poured into holes in concrete blocks after they are laid in place to improve the insulating quality of the construction. Perlite is also used as an insulator in other ways in the construction of buildings. It reduces noise and, since it is non-combustible, it also improves the fire resistance of different construction components in buildings.
Perlite is an important commodity in the horticulture industry where it is mixed with soil. The addition of perlite to soil increases the amount of air (i.e., oxygen) held in the soil, as well as the amount of water retained by the soil. This obviously improves the growing conditions for plants. This represents approximately 10% of annual perlite consumption.
Perlite is also used in a variety of different applications. For example, it is used as a filter for pharmaceuticals, chemicals, and beverages, and as a filler in the production of plastics and cements.
Substitutes and Alternative Sources
There are a number of materials that can be used in place of perlite for many of its applications. These materials (such as diatomite, pumice, expanded clay and shale, etc.) may be used in place of perlite without losing any of the benefits that perlite provides. Despite the lack of detailed information about world perlite production, there appears to be an abundant supply of perlite that will last many decades into the future.
- Common Minerals and Their Uses, Mineral Information Institute.
- More than 170 Mineral Photographs, Mineral Information Institute.
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