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Asbestos in Vermiculite and Other Building Materials

Alone, vermiculite is a fairly harmless mineral that has an interesting property; when heat is applied, it expands into a soft material that is useful for a number of different purposes. Over the years, vermiculite has been used as soil conditioner, absorbent packing material, and as insulation. As a form of rock, it is also fire resistant, and has been used for various types of fire stops. Vermiculite is still mined and processed in several places in the world, including Brazil, China, Russia and South Africa.

Starting in 1920s, vermiculite was marketed as an insulation product, which was sold under the proprietary brand name Zonolite®. Vermiculite had been discovered near the Libby asbestos mines in northwestern Montana. What the company management did not know - but which later became all-too-apparent - was that the Libby vermiculite was contaminated with a deadly form of amphibole asbestos, known as tremolite. The company that manufactured Zonolite® was eventually acquired by the W.R. Grace Corporation, one of the largest producers of asbestos products, in 1963.

Tremolite is among the most deadly of all asbestos fibers. Although never mined commercially, it is similar to crocidolite and amosite in the level of danger it poses to anyone inhaling it. Due to geologic factors, tremolite often occurs near vermiculite deposits; it is essentially formed by the same geologic processes. Today however, most vermiculite that is produced undergoes a thorough inspection for tremolite contamination before it is allowed on to the market.

Hazards Associated with Vermiculite Products

Although tremolite is one of the worst forms of asbestos in terms of health risk, many of the applications that vermiculite was used for were not applications where the end user would have much opportunity to inhale loose fibers. The primary risk from vermiculite was to the men and women in the mines producing it, as well as those working in the processing plants turning vermiculite into consumer and commercial products. Those individuals all inhaled tremolite in significant quantities, with very serious health effects. Inhalation of tremolite asbestos is conclusively linked to the development of lung cancer, asbestosis, pleural plaques, and malignant mesothelioma.



Bowker, Michael. Fatal Deception: The Untold Story of Asbestos (New York: Touchstone, 2003)

N/A. "About Vermiculite." The Vermiculite Association

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