Vermiculite Overview

Vermiculite is a group of minerals with a flaky, mica-like structure. It is mined for its uses in insulation and gardening. While vermiculite's toxicity has not been studied completely, to date no research has linked serious health effects with exposure to this mineral.

Mining site in Libby, Montana

Sample of vermiculite ore mined in Libby, Montana	Raw (right hand) and popped (left hand) vermiculite
(Photo source: U.S. Geological Survey and U.S. Environmental Protection Agency, Region 8, Denver, Colorado)

When heated, vermiculite exfoliates (or "pops"), forming a lightweight material ideal for packing, insulation, and as a soil additive. If the vermiculite is contaminated with asbestos, the exfoliation process releases asbestos fibers into the air.

Most vermiculite is not contaminated with asbestos. However, the vermiculite ore taken from a mining operation in Libby, Montana, is contaminated with asbestiform (asbestos-like) amphibole minerals, including the regulated forms tremolite and actinolite. It also contains forms that are not currently regulated, including winchite, richterite, and ferro-edenite. Research has linked all of the these forms to asbestos-related diseases.

Vermiculite was mined from Zonolite Mountain in Libby for more than 65 years (until 1990). The mine itself is approximately six miles from the town. A transfer facility was located approximately three miles from Libby. From the transfer facility, vermiculite was loaded on trains or trucks. Two expansion ("popping") facilities operated at different times within the town; these plants heated vermiculite to approximately 600 degrees Fahrenheit to expand the crystals. One of these facilities was next to a baseball field, which was readily accessible to the community's children.

The exfoliation process released asbestos fibers from the vermiculite ore into the air, where they could be inhaled. Inhalation of asbestos fibers suspended in air can result in lung diseases such as asbestosis, mesothelioma and lung cancer. The risk of developing any of these diseases depends on many factors, including the type of fiber, the level and duration of exposure, and the smoking history of the exposed individual. (See Health Effects of Exposure for more information.)

While current airborne asbestos levels in Libby now appear to be low, levels were certainly much higher during the many decades that vermiculite was actively mined, processed, and shipped. In fact, air concentrations up to 15 times current occupational limits were once reported for downtown Libby in the past.

Studies by the NIOSH and McGill University investigators found that former employees of the mine had substantial occupational exposure to these asbestiform minerals. These investigators documented pulmonary abnormalities and disease (asbestosis and lung cancer and mesothelioma) among employees. Cases of asbestos-related lung diseases have also been reported among people who lived with mine employees as well as others in the community.