Vermiculite is a naturally-occurring, metamorphic mineral belonging to the mica group of silicate minerals. Similar to the mineral asbestos, vermiculite is mined from raw ore deposits and processed worldwide for various industrial and construction products. In raw form, vermiculite may appear as shiny flakes. When processed, the mineral can be silver-gold, tan, green or gray-brown.

Vermiculite is mainly used in its processed form, after the mineral has been heated through a process known as exfoliation, or "popping." When rapidly heated, vermiculite transforms and recrystallizes due to a layer of water molecules contained within its structure. The water molecules are converted to steam and cause the mineral to expand to as much as 30 times its original size. This expanded form of vermiculite is lightweight, absorbent and a good insulator from heat and fire.

Asbestos in Vermiculite Compounds

Unfortunately, vermiculite mines can be sources of other minerals, too. Many vermiculite mines have been found to contain naturally-occurring asbestos. Vermiculite that has been contaminated with asbestos poses a significant health hazard to people who are exposed to airborne asbestos particles during any part of the mining or production processes, or to those who live near vermiculite mines or factories. While some asbestos-containing vermiculite mines have been shut down in recent years, many vermiculite products that contain asbestos are still in use today.

Uses for Vermiculite Compounds

Over the last century, vermiculite has been widely mined and processed worldwide for various construction, industrial and horticultural applications, as it is a superior insulator and filler material that is both lightweight and inexpensive.

Vermiculite has been used for the following applications:

Fertilizer carrier
Potting soil additive
Soil conditioner
Attic insulation (loose-fill, commonly sold under the product name Zonolite)
Acoustic finishes
Spray-on insulation
Concrete mixes for swimming pools
Stucco
Alternative to gypsum wallboard
Plasterboard
Packaging material (similar to styrofoam peanuts)
Fireproofing material
Whitewashes

Potential Hazards of Vermiculite

While vermiculite itself is not hazardous, the presence of other minerals such as asbestos or asbestos-like fibers in vermiculite compounds can pose a significant health hazard. The U.S. Environmental Protection Agency (EPA) and other regulatory agencies have discovered that certain vermiculite ore deposits in the U.S. may contain tremolite, actinolite or other types of asbestos fibers. The Agency for Toxic Substances and Disease Registry (ATSDR) has linked exposure to asbestos in vermiculite with adverse health effects such as lung disease, asbestosis and mesothelioma.

Asbestos fibers can be released from vermiculite during any stage of the mining, exfoliation or shipping processes, but the greatest danger is thought to exist during the exfoliation and processing step. When vermiculite is heated and expanded, asbestos fibers can be rapidly released into the air. If asbestos fibers are inhaled or ingested over long periods of time, the fibers can lodge in body tissues and remain in the body for many decades, causing serious health complications in later life.

Additionally, some vermiculite products may contain asbestos and pose a health hazard when used. For example, products such as vermiculite potting soil and gardening materials have been found to contain small amounts of asbestos during routine sampling tests by the EPA. If the asbestos fibers are loosened or otherwise disturbed, the fibers can easily become airborne.

Locations of Vermiculite Mines and Processing Plants

Vermiculite is mined worldwide, but the biggest producers of vermiculite today include the United States, South Africa, China, Japan and Russia. In the U.S., the largest vermiculite mines are found in South Carolina (Enoree and Woodruff), Virginia (Louisa County) and Montana (Libby, now closed). In 1998, there were as many as 20 vermiculite exfoliating plants in 11 states in the U.S.

Prior to 1990, more than 70 percent of the world's vermiculite was mined from Zonolite Mountain in Libby, Montana. The Libby mine operated from 1923 until 1990, when it was shut down due to the discovery of large amounts of asbestos in the mines. A 1984 study showed that raw vermiculite from Libby mines contained on average 3.5 to 6.4 percent asbestos by weight. When Libby vermiculite was actively being mined and processed, air quality reports for the downtown Libby area show that airborne asbestos fiber concentrations were up to 15 times the current safety limit.

Asbestos-containing vermiculite from the Libby mines was shipped around the U.S. to be processed and exfoliated. Processing sites where the contaminated vermiculite was shipped include:

Beltsville, MD
Dallas, TX
Dearborn, MI
Denver, CO
Easthampton, MA
Edgewater, NJ
Ellwood City, PA
Glendale, AZ
Hamilton Township, NJ
Honolulu, HI
Los Angeles, CA
Marysville, OH
Minneapolis, MN
Minot, ND
New Castle, PA
New Orleans, LA
Newark, CA
Omaha, NE
Phoenix, AZ
Portland, OR (N. Harding and N. Suttle)
Santa Ana, CA
Spokane, WA
St. Louis, MO
Tampa, FL
Trenton, NJ
Weedsport, NY
West Chicago, IL
Wilder, KY

Who May be at Risk for Asbestos Exposure

Those at highest risk for asbestos-related diseases from vermiculite exposure include individuals who worked in the vermiculite mines in Libby, Montana, for W.R. Grace and those who worked in processing plants where vermiculite was ground into powder or exfoliated. Vermiculite workers involved in the following processes may have been exposed to asbestos:

Mining
Milling
Exfoliating
Handling
Shipping

Individuals who lived with workers involved in the above-mentioned processes may also have been exposed to asbestos, as the fibers are easily carried home in hair, on clothing or on shoes. Residents who lived within the vicinity of vermiculite mines or vermiculite manufacturing sites may have been exposed to asbestos through the air.

Other occupations which may have been affected by asbestos-containing vermiculite include:

Construction workers
Demolition crews or remodelers
Homeowners

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