Vermiculite

by

Brad Black

• LAST MODIFIED: 28 July 2021
• DOI: 10.1093/obo/9780199756797-0205

Introduction

This series of articles should provide ample background to the story of vermiculite. It has served as a valuable commercial product over time, and continues to be mined, processed, and utilized around the world. For many years, vermiculite has been appreciated for its physical and chemical properties. Its physical properties, which allow expansion to a light density particle, make it suitable for light aggregate in concrete and other building materials and low heat transfer effective for insulation. The chemical properties which include an active cation exchange surface are ideal for agricultural products. Its natural formation is a micaceous mineral, composed of flat crystal plates arranged in a multi-laminate stack. Of great misfortune is the association of some vermiculite deposits with asbestiform amphibole formations. A remote Montana vermiculite deposit cohabitated with a large formation of these asbestiform minerals. Further complicating the situation is that this vermiculite deposit near Libby, Montana, produced a large majority of the world supply during the sixty-seven years of operation resulting in wide distribution of contaminated vermiculite. The epicenter of mining and processing was an isolated town where ongoing occupational and environmental exposures spanned throughout the years of mining operations. Morbidity and mortality studies recognize the pervasive adverse effects from amphibole exposure, not just in Libby, Montana, but also at export sites processing the vermiculite ore. Being the first population exposed to the unstudied asbestiform amphiboles winchite and richterite, there has been significant advancement in understanding their induced health effects. Studies in the toxicology of fibrous amphiboles and human health studies where a different pattern of asbestos-induced disease has been observed with Libby amphibole asbestos exposure have been completed. The observations have broadened our understanding of Libby amphiboles and enlightened us to the hazards of environmental exposure, and the long-term public health risk from existing contaminated vermiculite.