This article reviews the past 90 yr of scientific research directed on multiple aspects of the unique geology and environmental health issues surrounding the
vermiculite deposit found at Libby, MT. Hydrothermal alteration and extensive weathering of the ultramafic units resulted in the formation of a rich deposit of
vermiculite that was mined for 67 yr and used in numerous consumer products in its expanded form. Later intrusions of alkaline units caused hydrothermal alteration of the pyroxenes, resulting in formation of
amphiboles. Some of these
amphiboles occur in the asbestiform habit and have been associated with
pulmonary disease in former miners and mill workers. Identification of these
amphibole asbestos minerals has received little attention in the past, but recent work shows that the majority of the
amphibole mineral species present may not be any of the
amphibole species currently regulated by government agencies. Epidemiological studies on former miners have, nevertheless, shown that the
amphibole asbestos from the Rainy Creek igneous complex is harmful; also, a recent study by the Agency for Toxic Substances and Disease Registry shows that residents of Libby who had not been employed in the
vermiculite mining or milling operations also appear to have developed
asbestos-related
pulmonary diseases at a higher rate than the general public elsewhere. Since November 1999, the U.S. Environmental Protection Agency has been involved in the cleanup of
asbestos-contaminated sites in and around Libby associated with the mining and processing of
vermiculite.