Infrastructure and Construction Materials Guide — Perlite

Commodity Description

Perlite is a source of light-weight insulation material which “pops” or expands when heated to between 600 oC to 900 oC (1112 oF to 1652 oF) into an anhydrous (without water) glass foam. Ceiling tile, pipe insulation, cement foundation insulation, and potting soil additives containing expanded perlite are typical uses. As a form of volcanic silica glass, perlite is non-crystalline (amorphous).

Perlite is the single, and an important, replacement for asbestos post-1970 as a fire-resistant component in ceiling tile.

Photo by Bill Wilson

Geology and Mineralogy

Perlite is a silica glass found as a type of rhyolite often similar in chemistry and crystalline structure to other types of rhyolite such as pumice and obsidian. Common perlite with obsidian as an impurity contains ~0.1% to 0.4% molecular water. As volcanic lava cools, and with greater than 70% silica, the surface water evaporates and the molecular water is encapsulated in the perlite rock. When ground to a size of less than 6 mm (1/4 inch) and heated to a minimum temperature of 600 oC, the raw perlite expands into a usable material as a light, fluffy powder.

PRODUCTION AND PRICING

For U.S. production statistics and sale prices, “Perlite,” go to p. 132 of the USGS Commodity Summaries 2024.

For World Mine Production and Reserves, “Perlite,” go to p. 133 of the USGS Commodity Summaries 2024.

Uses

Uses include:

  • Fireproof insulating component of ceiling tile.

Typical ceiling tile containing expanded perlite

  • Expanded perlite mixed with clays and cementing additives for pipe insulation.
  • Raw perlite is expanded into white lightweight additive for potting soil to reduce clotting of high clay soils. The other main component of potting soils is expanded vermiculite that absorbs water and maintains moisture in the potting soil.

White expanded perlite in planting mulch

Perlite Microspheres

Most common perlite products range from 200 mesh (0.075 mm) to ¼ inch (0.64 mm) in diameter. A derivative product described as “microspheres” is produced in the range of 25 microns to 50 microns. This product was developed to be a key component in taping muds using paper strips to finish drywall installations. The microspheres serve to prevent cracking and splitting of the joints between large gypsum wallboard panels. One standard size and density for microspheres is 10% -100 mesh (0.150 mm) with an average particle size of 250 mesh (60 microns) and a bulk density of 112 to 144 g/m3.

Pressurized rail car, shipping of perlite microspheres    Photo by Bill Wilson

 

 

 

 

 

 

Substitutes

None for ceiling tile.
Horticultural: some vermiculite substitutes for some perlite in proprietary mixtures.

Major Producers

U.S.: IMERYS, Grefco
International: IMERYS, Chinese perlite companies

Mining Methods

All significant sized perlite deposits typically of at least one million tons or larger are mined by surface mining operations. Perlite deposits are relatively soft and can be removed by bulldozer and loaded with front-end loaders into trucks for transporting to a processing plant. When the processing plant is adjacent to the mine, conveyors are normally used instead of trucks.

Mineral Processing

Perlite processing plants all use a similar flowsheet. Mined perlite rock size as 12-inch by ½ inch sizes are processed by the following sequence: primary and secondary crushing; drying in a rotary dryer; classification by screening (single and double deck screens); and dust collection. Final product sizes range from -6 mesh (3.35 mm) to -200 mesh (0.075 mm), with surface moisture content less than 0.1% (or “bone dry”) and molecular-contained water in the crystal structure ideally 3.2% to 3.7%.

Environmental Factors

OSHA and MSHA view perlite dust as a nuisance material and simple dust-filtering face masks protect employees. Perlite has an amorphous, non-crystalline structure which has no effect on human lungs and is expelled by a simple cough. Additionally, perlite is universally used as a safe ceiling tile component that replaced asbestos as the fireproof component in construction materials.

References

United States Geological Survey (USGS) Commodity Summaries 2023. https://pubs.usgs.gov/publication/mcs2023. The 2023 summary reports 2022 statistics.

United States Geological Survey (USGS) Commodity Summaries 2024.  https://pubs.usgs.gov/publication/mcs2024. 2024 version reports 2023 statistics.