Tremolite

Abstract: Thirty samples of amphibole-rich rock from the largest mined vermiculite deposit in the world in the Rainy Creek alkaline-ultramafic complex near Libby, Montana, were collected and analyzed. The amphibole-rich rock is the suspected cause of an abnormally high number of asbestos-related diseases reported in the residents of Libby, and in former mine and mill workers. The amphibole-rich samples were analyzed to determine composition and morphology of both fibrous and non-fibrous amphiboles. Sampling was carried out across the accessible portions of the deposit to obtain as complete a representation of the distribution of amphibole types as possible. The range of amphibole compositions, determined from electron probe microanalysis and X-ray diffraction analysis, indicates the presence of winchite, richterite, tremolite, and magnesioriebeckite. The amphiboles from Vermiculite Mountain show nearly complete solid solution between these end-member compositions. Magnesio-arfvedsonite and edenite may also be present in low abundance. An evaluation of the textural characteristics of the amphiboles shows the material to include a complete range of morphologies from prismatic crystals to asbestiform fibers. The morphology of the majority of the material is intermediate between these two varieties. All of the amphiboles, with the possible exception of magnesioriebeckite, can occur in fibrous or asbestiform habit. The Vermiculite Mountain amphiboles, even when originally present as massive material, can produce abundant, extremely fine fibers by gentle abrasion or crushing.

Abstract: The prograde, high pressure, transition from antigorite serpentinite to enstatite-olivine rock occurs along a tectonically undisturbed profile at Cerro del Almirez, SE Spain. The reactant assemblage is antigorite + olivine with tremolite rimming precursor diopside. The product assemblage of tremolite + chlorite + enstatite + olivine has a spinifex-like texture with arborescent or radiating olivine elongated parallel to [001] and with radially grown enstatite. Product enstatite is very poor in Al2O3. Due to numerous oriented submicroscopic inclusions of chromian magnetite, product olivine has a brownish pleochroism and a bulk chromium content similar to precursor antigorite. Titanian clinohumite with a fluorine content of 0.45–0.50 wt% persisted beyond the breakdown of antigorite. The partitioning of iron and magnesium amongst the silicate phases is almost identical to that at lower pressures. Average Kd values Mn/Mg and Ni/Mg are 0.17 and 0.70 for antigorite-olivine pairs and 1.83 and 0.22 for orthopyroxene-olivine pairs, respectively. These data are useful in discriminating generations of olivine grown on each other. From the field data a phase diagram topology for a portion of the system CaO-MgO-SiO2-H2O is derived. This topology forms the basis for extrapolations into inaccessible P-T regions.

Abstract: Vermiculite is a naturally occurring mineral mined in the United States, Brazil, Argentina, Mexico, South Africa, Zimbabwe, Kenya, Uganda, Egypt, India, Russia, China, Japan, and Australia. Mined vermiculite ore is milled to produce vermiculite concentrate of various sizes and grades. When rapidly heated, vermiculite concentrate expands to form small, light-weight, accordion-shaped granules. Vermiculite is used in construction products (loose-fill attic insulation, acoustic finishes, spray-on fireproofing, gypsum plaster, concrete mixes for swimming pools), consumer products (packing materials, adsorbent in laboratories), agricultural and horticultural products (animal feed, bulking agent, fertilizers, pesticides, seed encapsulant, hydroponics, potting mixes, soil conditioners), and in industrial products (brake shoes and pads, drilling muds, furnaces, filters, insulator blocks, paints, and sealants) [U.S. Environmental Protection Agency (EPA) 2006]. Vermiculite from the mine that operated near Libby, Montana, from the early 1920s until 1990 was contaminated with asbestos and other fibrous amphibole minerals, crystalline silica, and talc. The U.S. Geological Survey has characterized the respirable fraction of asbestiform amphiboles contaminating the Libby vermiculite as approximately 84% winchite, 11% richterite, and 6% tremolite (Meeker et al. 2003). The raw Libby ore was estimated to be 21–26% asbestos by weight; the mill feed was 3.5–6.4% asbestos; airborne dust in the dry mill was 40% asbestos (Wake 1962); and the vermiculite concentrate shipped to numerous processing plants in the United States and other countries was 0.3–7.0% asbestos before expansion (Amandus et al. 1987; Atkinson et al. 1981). Previous studies of Libby workers documented increased risk of lung cancer and nonmalignant respiratory disease among highly exposed workers with at least 1 year tenure (Amandus and Wheeler 1987; McDonald et al. 1986, 2004). Reports of respiratory disease mortality among community residents and household contacts of Libby vermiculite workers suggested increased risk from transient exposure or ambient community exposure [Agency for Toxic Substances and Disease Registry (ATSDR) 2002; Schneider 1999]. Cross-sectional radiographic screening conducted in Libby for the ATSDR revealed that 6.7% of community residents with no occupational or familial exposure have radiographic evidence of asbestos-related disease (Peipins et al. 2003). These findings suggest that risk from asbestos-contaminated vermiculite may not be limited to those with high-intensity occupational exposure. This report expands the previously studied occupational cohort to include all white men hired at Libby from September 1935 through December 1981. The intent here is to describe the mortality experience of workers exposed to Libby amphibole fibers (tremolite asbestos, winchite, richterite) over the full range of exposure and employment duration. Occupational respiratory disease mortality among Libby workers is compared to that expected based on the mortality experience of the U.S. population, and standardized mortality ratios (SMRs) and standardized rate ratios (SRRs) for asbestosis, lung cancer, and all nonmalignant respiratory diseases are presented.

Abstract: Lung tissue samples from 78 cases from autopsy of mesothelioma in Canada, 1980 through 1984, and from matched referents were examined by optical and analytical transmission electron microscopic study. Concentrations of amosite, crocidolite, and tremolite fibers, and of typical asbestos bodies discriminated sharply between cases and referents. The distributions of chrysotile and anthophyllite/talc fibers and of all other natural and man-made inorganic fibers (greater than or equal to 8 microns) in the two series were quite similar. Relative risk was related to the concentration of long (greater than or equal to 8 microns) amphibole fibers with no additional information provided by shorter fibers. The proportion of long fibers was much higher for amphiboles than chrysotile and, except for chrysotile, systematically higher in cases than referents. Amphibole asbestos fibers could explain most mesothelioma cases in Canada and other inorganic fibers, including chrysotile, very few. Fibrous tremolite, contaminant of many industrial minerals including chrysotile, probably explained most cases in the Quebec mining region and perhaps 20% elsewhere.