Characterization of tremolite asbestos from Cemetery Ridge, Arizona and anthophyllite asbestos from Palm Springs,...

Well-characterized asbestos mineral samples are required for use as analytical standards and in future research projects. Even in areas where asbestos is no longer mined it can still be encountered in mine spoil, when rocks are disturbed by construction projects, and in other mineral products (eg talc and vermiculite), as well as in products made from asbestos and in uncontrolled disposal of those products. While chrysotile was the type of asbestos most commonly mined and used in the United States, amphibole (tremolite and anthophyllite) asbestos is widespread and was also extracted commercially for the manufacture of specific products. Analysts are called upon to recognize the varieties of asbestos when they are encountered. Amphibole asbestos exhibits variation in crystallinity and chemistry, and so it is important that samples where the range of these features is well-described are available. Tremolite and anthophyllite are important constituents of certain rock types, and both can occur in fibrous and nonfibrous crystal habits, and crystallinity and chemistry vary between and within occurrences. Therefore, it is useful to have available a range of samples exhibiting this variation as a reference for analysts and researchers. Tremolite asbestos from an abandoned mine at Cemetery Ridge, Arizona, and anthophyllite asbestos from an abandoned mine near Palm Springs, California, were analyzed using (i) a polarized light microscope with a determination of principal optical properties, (ii) spindle stage analysis using a polarized light microscope to determine whether individual fibers and bundles of the samples were polycrystalline or single-crystal cleavage fragments, (iii) x-ray diffraction, (iv) a transmission electron microscope, including energy dispersive x-ray spectroscopy, and selected area electron diffraction, and (v) electron probe microanalysis. Additional images were acquired with a field-emission scanning electron microscope and transmission electron microscope to show the diversity of appearance. The overall findings of the study indicate that the materials are tremolite asbestos and anthophyllite asbestos. The tremolite asbestos is asbestiform tremolite with some prismatic crystals and cleavage fragments. The following formula was determined from electron probe microanalysis:Na0.01(Ca1.95Fe0.04Mn0.02)∑2.00(Mg4.65Fe0.39Al0.01)∑5.00(Si7.98Al0.02)∑8.00O22(OH)2 The atomic ratio (Mg)/(Mg + Fe) is 0.915, which falls into the compositional range for tremolite, but it is close to the boundary with actinolite (ratio < 0.90), and it is possible that compositional variation between individual grain analyses may report results as actinolite. Accessory quartz was also noted, but in only small quantities (<5%). The anthophyllite asbestos is asbestiform anthophyllite with some prismatic crystals and some accessory minerals. The following formula was determined from electron probe microanalysis:□(Mg1.04Fe0.80Ca0.054Mn0.044)∑1.94(Mg4.98Al0.02)∑5.00Si8.03O22(OH)2Accessory hydrated silicate minerals (talc and chlorite) are also present, but in only small quantities. Materials for research use were prepared by sorting, acid-washing, and mixing for subdivision into vials of approximately 10 g each. The samples can be obtained from Research Triangle Institute (RTI International, Research Triangle Park, NC, United States) on request.