Amphibole asbestos from Libby, Montana: Aspects of nomenclature

Richterite-asbestos and winchite-asbestos are not listed in the federal reg ulations governing asbestos. However, asbestiform winchite is found in the gangue at the Libby, Montana, vermiculite deposit, where asbestos-related d iseases have been reported among the miners and millers. Changing amphibole nomenclature, uncertainties in Fe2+/Fe3+, and natural compositional variab ility result in samples of the asbestiform amphibole from Libby being varia bly classified as soda tremolite, richterite, sub-calcic actinolite, and wi nchite. A classification of winchite-asbestos is assigned for two samples o f Libby asbestos analyzed for this report, consistent with the most recent International Mineralogical Association classification system. Although som e of the unit-cell parameters and optical properties reported here are dist inctive, others are very similar to the tremolite-actinolite series.