Mineral Resource of the Month: Vermiculite

by U.S. Geological Survey
Tuesday, September 2, 2014

Arnold O. Tanner, a mineral commodity specialist for the U.S. Geological Survey, compiled the following information on vermiculite, which is used in construction and horticulture.

Vermiculite comprises a group of hydrated, laminar magnesium-aluminum-iron silicate minerals resembling mica. They are secondary minerals, typically altered biotite, iron-rich phlogopite or other micas or clay-like minerals that are themselves sometimes alteration products of amphibole, chlorite, olivine and pyroxene. Vermiculite deposits are associated with volcanic ultramafic rocks rich in magnesium silicate minerals, and flakes of the mineral range in color from black to shades of brown and yellow. The crystal structure of vermiculite contains water molecules, a property that is critical to its processing for common uses.

Using a process called exfoliation — in which vermiculite flakes are heated to 900 degrees Celsius or higher, causing water within the flakes to flash to steam and expand — crude vermiculite ore is processed into particles that are eight to 20 times larger. The resulting lightweight material is chemically inert and fire resistant, with low density and low thermal conductivity. It is also odorless, has high liquid absorption capacity and catalytic properties.

Because it is lightweight and thermally insulating, vermiculite is used in general building plasters and concrete products, alone or combined with other lightweight aggregates such as perlite. Special plasters, in which vermiculite is combined with binders like gypsum or portland cement, fillers or other additives, provide fire protection and soundproofing. As insulation, exfoliated vermiculite, sometimes treated with a water repellent, is used to fill pores and cavities in masonry construction and hollow blockwork to enhance acoustic properties, fire rating and insulation performance. Exfoliated vermiculite can also be used to produce refractory and insulation concretes and mortars, and to make high-temperature binders for construction materials, gaskets, specialty papers, textiles and vehicle brake linings. Finer grades of exfoliated vermiculite can be used to produce various shapes of insulation pellets, high-temperature insulation, as a primary component in cementitious coatings, and as a filler in inks, paints, plastics and other materials.

Vermiculite can absorb liquids such as fertilizers, herbicides and insecticides, which can then be transported as free-flowing solids. It is used in the fertilizer and pesticide markets because of its ability to act as a bulking agent, carrier and extender. In horticulture, exfoliated vermiculite improves soil aeration and moisture retention, and when mixed with peat or other composted materials, such as pine bark, vermiculite produces a good growing medium for plants. As a soil conditioner, exfoliated vermiculite improves aeration in clay-rich soils and water retention in sandy soils, while reducing the likelihood of compaction, cracking and crusting of the soil.

For more information on the commercial use of vermiculite, visit minerals.usgs.gov/minerals/.


In 2013, about 100,000 metric tons of vermiculite concentrate and about 65,000 metric tons of exfoliated vermiculite were produced in the United States.

World mine production of vermiculite was an estimated 420,000 metric tons in 2013. South Africa, the United States, Brazil and China were the leading producers.

In the United States, 50 percent of vermiculite is used in agriculture/horticulture; 20 percent is used in lightweight aggregates; 5 percent is used to make insulation; and 25 percent goes to other uses.


The name vermiculite comes from the Latin “vermiculus,” meaning larva or small and worm-like, or “vermiculare,” meaning to breed worms, for its characteristic look when undergoing exfoliation.

Prior to Thomas H. Webb’s work in the early 19th century, vermiculite was known for many years in Japan as a children’s novelty.

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