Reconnaissance Study of the Geology of U.S. Vermiculite Deposits - Are Asbestos Minerals Common Constituents?

Unusually high incidences of asbestos-related mortality and respiratory disease in the town of Libby, Montana, have been linked to amphibole mineral fibers intergrown with the vermiculite deposits mined and milled near the town from 1923 to 1990. Prompted by this discovery, the U.S. Geological Survey undertook an investigation of the mineral content of other U.S. vermiculite deposits to determine if the amphibole asbestos minerals like those found in the Libby deposits are common in other vermiculite deposits. This site discusses the preliminary results of that study and the conclusion that the asbestiform amphibole mineralogy of the Libby deposit is not unique, and that vermiculite deposits associated with zoned, alkalic/calcic, quartz-poor plutons, especially those with characteristics of carbonatite intrusions, may be likely to contain fibrous amphiboles. Educational levels: Graduate or professional, Undergraduate upper division