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Erionite is a naturally occurring fibrous mineral found in many parts of the world, including the western United States. Inhalational exposure to erionite fibers in some localities is associated with health effects similar to those caused by asbestos exposure, including malignant mesothelioma. Therefore, there is concern regarding occupational exposures in the western United States. Currently, there are no standard sampling and analytical methods for airborne erionite fibers, as well as no established occupational exposure limits. Due to the potential adverse health effects, characterizing and minimizing exposures is prudent. Crystalline silica also occurs naturally in areas where erionite is found, principally as the mineral quartz. Work activities involving rocks containing quartz and soils derived from those rocks can lead to exposure to respirable crystalline silica (RCS). The typically dry and dusty environment of the western United States can increase the likelihood of exposures to aerosolized rocks and soils, but inhalation exposure is also possible in more humid conditions. In this case study, we describe several outdoor occupational environments with potential exposures to erionite and RCS. We describe our method for evaluating those exposures and demonstrate: (1) the occurrence of occupational exposures to airborne erionite and RCS, (2) that the chemical make-up of the erionite mineral can be determined, and (3) that effective dust control practices are needed to reduce employee exposures to these minerals. [ABSTRACT FROM AUTHOR]

Liquidus to near-solidus phase relations between 0.8 ad 12.0 GPa and 900 and 1200°C were determined for an SiO2-rich lamproite from Smoky Butte, Montana. At 7–10 GPa, assemblages between liquidus and solidus are clinopyroxene+garnet, garnet+clinopyroxene+coesite, garnet+clinopyroxene+coesite+rutile+K–Ti silicate, and garnet+clinopyroxene+K–Ti silicate+phlogopite+coesite+rutile. At 12 GPa, comparable assemblages are garnet, garnet+clinopyroxene+coesite, and garnet+clinopyroxene+K silicate+coesite+rutile. At 6–12 GPa, K–Ti silicates and K–Ba phosphate compounds occur between 1200 and 1400°C. At 12 GPa, K silicate replaces the K–Ti silicate compound present at lower pressures. At >6 GPa, clinopyroxene and garnet incorporate K in their structures, particularly at lower temperatures. Near-liquidus phase relations of the Smoky Butte lamproite are compared with those of previously investigated lamproite of a similar composition. It is considered unlikely that near-liquidus garnetite mineral assemblages at 7–12 GPa could reflect the source of these magmas. A more likely source for these SiO2-rich lamproitic magmas is an assemblage comparable with the near-solidus assemblage of garnet+clinopyroxene+phlogopite and minor K-, Ti-, Ba-enriched compounds. On partial melting such an assemblage would yield a composition comparable with that of the SiO2-rich magma from Smoky Butte. SiO2-rich lamproite magmas may be primary melts from an enriched source from deep in the lithospheric mantle. [ABSTRACT FROM AUTHOR]