CHEMISTRY AND MORPHOLOGY OF AMPHIBOLE ASBESTOS FROM LIBBY, MONTANA: IMPLICATIONS FOR THE HEALTH, MINERALOGIC, AND REGULATORY COMMUNITIES

Asbestos is a commercial term applied to seven regulated minerals that occur in asbestiform habit. Six of these minerals are members of the amphibole group. Regulators and health experts use commercial nomenclature for these amphiboles. Mineralogists classify amphiboles by a system based on crystal site chemistry that often assigns different mineral names. This dual system of nomenclature is problematic for the regulatory, health and mineralogic communities because within any single geologic occurrence or locality, amphibole compositions can vary substantially. This is certainly true for the amphiboles from the Rainy Creek Complex at Libby, Montana. Libby amphiboles include tremolite and actinolite asbestos, but also several more unusual, and unregulated varieties such as winchite and richterite asbestos. Electron probe microanalysis reveals that these phases are in complete solid solution and are intermingled at the micrometer scale. In addition to chemical variability, the Libby amphiboles exhibit a wide range of regulated and unregulated morphologies from truly asbestiform to blocky, non-fibrous grains. Asbestiform fibers, acicular particles, particles showing curvature, and cleavage fragments are all found in the Libby amphibole. These different chemistries and morphologies, intermingled at the micron scale, may each possess unique properties that could influence how they behave within the respiratory and gastro-intestinal systems and how they are regarded in regulatory assessments. It is well known that inhalation of asbestiform mineral dust is a causative factor for diseases such as asbestosis and mesothelioma. However, the mechanisms of disease development following asbestos insult are presently unclear. Recent findings indicate that certain morphologies as well as chemical and surface properties may play a significant role in disease development. The ultimate understanding of these mechanisms will require close collaboration between toxicologists and mineralogists.