Perlite

Perlite is an amorphous (with no defined crystalline form) volcanic glass (silica or SiO₂) that has relatively high water content, typically formed by the hydration of obsidian. Perlite has the unusual characteristic of expanding and becoming porous when it is heated.  It can expand to as much as twenty times its original volume.  Expansion occurs when the glassy lava rock is heated to 1600 degrees F (871 degrees C) and the water molecules trapped in the rock turn into vapor, causing the rock to expand.  (This is the same principle as the water in popcorn 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.

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Description

Perlite is an amorphous volcanic glass (SiO₂) that has relatively high water content, typically formed by the hydration of obsidian. Perlite has the unusual characteristic of expanding and becoming porous when it is heated.  It can expand to as much as twenty times its original volume.  Expansion occurs when the glassy lava rock is heated to 1600 degrees F (871 degrees C) and the water molecules trapped in the rock turn into vapor causing the rock to expand.  (This is the same principle as the water in popcorn 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.

Relation to Mining

Perlite is typically mined in surface mines through ripping (breaking with a toothed attachment to a bulldozer) or blasting, or both. If the perlite is soft and crumbles easily, is brecciated (composed of angular fragments), or extensively jointed, ripping is employed with significant cost savings. Blasting is required where perlite cannot be readily broken using rippers, but care must be taken to achieve fragmentation without production of excessive fines (finely crushed) or oversized material. Once broken and sometimes crushed, the perlite is loaded on trucks or conveyor belts by front-end loaders, excavators, or scrapers for transport to the processing plant. Selective mining is used to minimize associated rhyolite or obsidian. If perlite textures vary, it is often blended to produce consistent milling characteristics and to meet market specifications.

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. Other countries that produce large amounts of crude and expanded perlite include China, Greece, Italy, Philippines, Mexico and Turkey.

Uses

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. Perlite is also used as an insulator to reduce 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 oxygen held in the soil, as well as the amount of water retained by the soil. This represents approximately 10% of annual perlite consumption.