Vermiculite (mineral)
Vermiculite is a naturally occurring mineral that belongs to a group of hydrated aluminum-iron magnesium silicates. Known for its unique ability to expand into long, wormlike strands when heated—a process called exfoliation—it is widely used in various industries, including construction, agriculture, and horticulture. Commercially mined in countries such as Australia, Brazil, China, and the United States, vermiculite is valued for its lightweight, fire-resistant, and chemically inert properties.
Primarily, vermiculite is utilized as insulation, soil conditioner, and packaging material for hazardous substances. In agriculture, it enhances soil aeration and moisture retention, making it beneficial for potting mixes and hydroponics. In construction, it is incorporated into insulation products and fireproofing materials. Although there have been instances of vermiculite being contaminated with asbestos, the mineral itself is generally recognized as safe by authorities like the U.S. Food and Drug Administration. With a history dating back to the early 19th century, vermiculite continues to play a significant role in both residential and industrial applications.
Vermiculite (mineral)
Where Found
Vermiculite is found in various parts of the world. Commercial mines for vermiculite are located in Australia, Brazil, China, Russia, Kenya, Zimbabwe, South Africa, and the United States.
Primary Uses
Vermiculite has a number of applications in a variety of industries. Some uses for vermiculite include construction, agricultural, and horticultural applications. It is also used as fire protection, as insulation, and in various industrial markets. Vermiculite is used as packaging material for safe shipment of hazardous compounds. Recent uses include nanocomposites for films and coatings.
Technical Definition
Vermiculite is the geological name given to a large group of hydrated laminar, or layered, minerals that are aluminum-iron magnesium silicates that resemble mica in appearance. Vermiculite is a member of the phyllosilicate group of minerals, a group with the characteristic property of expanding into long, wormlike strands with heating. This expansion process is called exfoliation and forms the basis for commercial use of the mineral.
Commercial vermiculite typically contains 38 to 46 percent silicon dioxide (SiO2), 16 to 35 percent magnesium oxide (MgO), 10 to 16 percent aluminum oxide (A12O3), 8 to 16 percent water, and smaller amounts of several other chemicals. When vermiculite is heated and expanded, a color change occurs that depends on the chemicals present and the temperature of the furnace. Generally, however, vermiculite is gold-brown in color. When vermiculite is heated, it increases ten to thirty times in volume. The bulk density of crude vermiculite is approximately 640 to 1,120 kilograms per cubic meter. Depending on the size of the granules, the bulk density of expanded vermiculite is about 64 to 160 kilograms per cubic meter.
Description, Distribution, and Forms
The name vermiculite is derived from a combination of the Latin word vermiculare, meaning “to breed worms,” and the English suffix “-ite,” which means mineral or rock. The term “vermiculite” applies to a group of minerals that have the property of expanding into long, wormlike particles when heated. When vermiculite ores exfoliate, they expand to many times their original volume.
There are two key components of vermiculite’s unique properties. First, vermiculite has a laminar, or layered, crystalline structure with connected layers that expand or unfold linearly, like an accordion. The second key component is trapped water held within vermiculite. When vermiculite is heated, this water is rapidly converted into steam, which forces the layers to separate and open, or exfoliate. After exfoliation, the lightweight material that results is chemically inert, fire-resistant, and odorless. In its expanded form, vermiculite has very low density and thermal conductivity, which makes it useful in many applications. The surface area of exfoliated vermiculite is large and chemically active, a feature that makes it useful in some chemical processes as an absorbent.
Several naturally occurring vermiculite minerals and soils exist, and the identification of specific ones requires scientific analysis. One of the common forms of vermiculite, however, is known as commercial vermiculite. This is the form that is mined and processed for various industrial and residential uses. Vermiculite ores from mines are derived from rocks that contain large crystals of the minerals biotite and iron-bearing phlogopite. Chemically, vermiculite is a hydrated magnesium aluminum silicate.
All vermiculite ores contain a range of other minerals that were formed along with the vermiculite in the rock. Although vermiculite ores from some sources have been found to contain asbestos, asbestos is not intrinsic to vermiculite. Only a few vermiculite ores have been found to contain asbestos and generally not more than trace amounts. One vermiculite mine, in Libby, Montana, was found to be contaminated with substantial amounts of asbestos and was subsequently closed down. Overall, vermiculite is classified a “generally recognized as safe” (GRAS) mineral, a designation bestowed by the U.S. Food and Drug Administration.
History
Most accounts indicate that vermiculite and its unique properties were known as early as 1824, when Thomas Webb experimented with the mineral in Worcester, Massachusetts. During his experimentation, he observed that heating the mineral resulted in the formation of long, wormlike particles. Because of this property, he named the mineral vermiculite, or worm breeder, because the heated mineral looked like a mass of worms. Other accounts suggest that vermiculite was discovered in 1881 in Libby, Montana, by gold miners, and that in 1919, Edward Alley discovered its unique properties.
Vermiculite was thought to be mostly a scientific curiosity until the early 1900’s, when more practical uses for the mineral were discovered. In 1915, the first commercial mining effort of vermiculite was initiated in Colorado, where the mineral was sold as tung ash. There were not enough buyers, however, and the mining effort failed. The Zonolite Company started the first successful vermiculite mine in 1923 in Libby, Montana. In 1963, W. R. Grace bought the Zonolite mine, which continued to operate until 1990. While in operation, this mine produced about 80 percent of the world’s vermiculite supply. Vermiculite from the Libby mine was found to be contaminated with a toxic form of naturally occurring asbestos.
Obtaining Vermiculite
Obtaining vermiculite requires mining. There are many commercial mining operations throughout the world. Locations of some of the predominant commercial mines are in Australia, Brazil, China, Kenya, South Africa, the United States, and Zimbabwe. As of 2009, the largest vermiculite mining operation in the world was located in the Phalaborwa, or Palabora, region of northeastern Transvaal in South Africa. Other large mining operations are located in the northwestern corners of China and in the United States, along the eastern Appalachian range (in Virginia and South Carolina). Some other countries producing significant amounts of vermiculite include Russia, Brazil, and Japan.
Vermiculite mines are surface operations in which ore is separated from other minerals. Rocks containing vermiculite are detonated and the loose rocks are fed through crushers and screens to separate the vermiculite from surrounding rocks. Vermiculite flakes are shipped to exfoliation plants, where they are heated in a furnace to approximately 540° to 810° Celsius, which causes trapped water to convert rapidly to steam and vermiculite flakes to expand into wormlike particles. Vermiculite ores may also contain other materials, such as mica, quartz, feldspar, and possibly asbestos. None of the mines in operation poses an asbestos health risk.
Uses of Vermiculite
Vermiculite has thousands of applications in a variety of industries and has been in use for more than eighty years. Vermiculite is used in construction, agricultural, horticultural, and industrial markets. It has applications ranging from use as building insulation to improving potting soil. It is used by pool contractors, by greenhouse growers, in fireproofing, and in many other commercial businesses.
Vermiculite has been used extensively as a soil conditioner and as an amendment in potting soils. It is used in soil mixes for root cuttings, seed germination, turf grass, plantings, and gardens. Recently, vermiculite has been used increasingly in hydroponic gardening and for water conservation. Vermiculite improves soil aeration and drainage, while retaining moisture and nutrients necessary for plant growth. Vermiculite is readily mixed with soil, peat, composted bark, and organic compost and creates air channels to allow the soil mix to breathe, while at the same time holding water and nutrients needed by the plant. When used as a carrier for fertilizers, pesticides, or herbicides, or as a bulking agent, vermiculite ensures better distribution. Vermiculite has cation exchange properties, which help the growing plant access necessary nutrients such as ammonium, potassium, calcium, and magnesium. In the agricultural industry, vermiculite is used in animal feed as a carrier for supplements and nutrients.
In construction, vermiculite is used in acoustic finishes, in lightweight insulating concrete, in gypsum plaster, and as loft insulation and fire protection. Vermiculite can be used in combination with many typical binders, such as portland cement, clay, gypsum, and resins. In pools, vermiculite has been used in place of packed sand. Vermiculite has been used as loose-fill insulation in insulated masonry wall systems and as a lightweight aggregate for plaster by mixing with either gypsum or portland cement. Vermiculite is a major ingredient in most fireproof door cores and safes. Vermiculite is ideal for filling gaps or spaces in existing insulation and was one of the first home insulation products used in the United States. When ground into a powder, vermiculite is useful as filler in paints, plastics, and other materials.
The absorption properties of vermiculite make it useful as an absorbent packaging material for safe shipment of hazardous liquids. It can hold liquids such as oils, nutrients, chemical mixtures, and special coatings. It is also used to transport liquids such as fertilizers, herbicides, and insecticides, as free-flow solids. Vermiculite is also used to insulate cryogenic tanks. Vermiculite is used in fixation of hazardous material and for nuclear-waste disposal. In the automobile industry, vermiculite is used in brake pads and shoes.
Bibliography
Kogel, Jessica Elzea, et al., eds. Industrial Minerals and Rocks: Commodities, Markets, and Uses. 7th ed. Littleton, Colo.: U.S. Society for Mining, Metallurgy, and Exploration, 2006.
Middleton, Gerald V., et al. Encyclopedia of Sediments and Sedimentary Rocks. New York: Springer, 2003.
Prothero, Donald R., and Frederic L. Schwab. Sedimentary Geology: An Introduction to Sedimentary Rocks and Stratigraphy. 2d ed. New York: Freeman and Company, 2004.
Velde, Bruce. Origin and Mineralogy of Clays. New York: Springer, 1995.
The Vermiculite Association.