ABSTRACT LXXVII, SEPTMBER 2008 n.2:

Abstract - Fluoro-edenite crystals from Biancavilla, a mineral characterized by various cations in different crystallographic sites, have been studied with Electron Microprobe Analysis (EMPA) and micro-Raman spectroscopy. The spectroscope used in this study was fitted with an optical microscope equipped with two polarizers and a rotating plate with a vernier, allowing precise orientation of the sample. The Raman spectra were acquired after precisely aligning the crystals with respect to the incident laser beam. The spectra recorded are discussed in relation to the chemical data from EMPA analyses. This investigation suggests that a similar methodological approach can be used to discriminate other fibrous amphiboles which can be difficult to identify by conventional techniques

Matthew S. Sanchez and Mickey E. Gunter - Tests of the correlation between composition and morphology of tremolite from Montgomery County, Maryland, USA.

Abstract-Polished thin sections were prepared of a sample of tremolite from Montgomery County, Maryland and analyzed for major and trace elements of the prismatic and fibrous morphologies. Chemical data were obtained using EPMA (major element), laser ablation ICP-MS (trace element), XRF (whole rock), and the Fe³⁺/EFe ratio was determined by Mössbauer spectroscopy. The polished thin sections were observed with a polarized light microscope (PLM) and photographed to show the textural relationships between the prismatic and fibrous amphiboles. Powder X-ray diffraction (XRD) showed that the sample is a relatively pure tremolite with only traces of clinochlore occurring in the sample. The variation of major elements in the prismatic crystals is less than the variation among the fibrous portion, while the variability in the level of trace elements is greater for the prismatic crystals than the fibrous portion. Multivariate hierarchal cluster analysis was performed in an attempt to correlate composition to morphology. Using the major elements obtained by EPMA, no clustering occurred, while the trace elements obtained from laser ablation ICP-MS, yielded a separation based on morphology.

Aneta Maria Zakrzewska, Pietro Paolo Capone, Antonino Iannň, Vincenzo Tarzia, Antonella Campopiano, Egidio Villella and Renato Giardino - Calabrian ophiolites: dispersion of airborne asbestos fibers during mining and milling operations.

Abstract-Calabrian ophiolitic deposits find industrial uses in two areas depending on the conditions of the deposit: the first exploits the friability of rocks, to obtain the aggregate used in local concretes, while the second use consists of the production of the massive blocks of stones used for decorative elements, frames, paving, flooring, lapidary and jewels art, etc. We selected these two mining and milling methods to gain an understanding of their operations with the aim of assessing the risk of the worker’s exposure to asbestos airborne fibers, and the possible dispersion of such fibers in the surrounding environment. Also, the working cycle relative to the production of lapidary material was investigated in order to assess the risk of the worker’s exposure to airborne asbestos fibers. Furthermore, both squares and streets of the urban districts near the ophiolites quarries and milling plants were investigated by air sampling to determine the possible dispersion of asbestos fibers into these populated areas. Samples were collected onto membrane filters and analysed using Scanning Electron Microscopy (SEM). The qualitative characterisation of the fibers was carried out by Energy Dispersive Spectroscopy (EDS). The results show that the highest values of the mean tremolite fiber concentrations are obtained during the diamond wire cutting operation (0.071 fiber/cm3) and the brooming process (0.059 fiber/cm3). Furthermore, about 42% of the respirable asbestos fibers are released during the cutting operations. Even though the worker’s exposure to tremolite fibers did not exceed the regulatory limit specified, they should be supplied with suitable personal protection equipment in order to reduce asbestos risk exposure. Furthermore, the workers should be educated and informed about the risks relating to occupational exposure to asbestos fibers. The asbestos fiber concentrations obtained by environmental samplings performed in the urban districts do not exceed the limit of 1 fiber/litre, as World Health Organization recommends for urban areas. However, in order to reduce the dispersion of tremolite fibers the best available techniques should be adopted and used to reduce exposure.

Mickey E. Gunter and Matthew S. Sanchez- Amphibole content of commercial vermiculites by powder X-ray diffraction.

Abstract - Seven commercial expanded vermiculite products were obtained and a powder X-ray diffraction method used to determine if they contained amphibole, and if so, what quantity. Of the seven, two contained approximately 0.2 and 0.5% amphiboles, while two others had no detectable amphiboles; the lower detection limit is 0.05 to 0.10% for this method. The remaining three samples showed levels of amphiboles that are within our lower detection range. USEPA had conducted a similar test by TEM and our results are in agreement with theirs. The methods discussed herein should be used for unbiased detection of amphiboles in bulk samples, and supplemented, when significant amounts of amphiboles are found, by microscopic methods to determine the morphology of the amphibole particles.

J. Craig Huntington, John J. Ptasienski, Kristin L. Bunker, Brian R. Strohmeier,Drew R. Van Orden and Richard J. Lee- A new method for fracturing mineral particles for cross-sectional FESEM analysis.

Abstract - Cross-sectional samples of mineral particles observed in a field emission scanning electron microscope (FESEM) can provide information on their shape, dimensions, and crystal growth that is difficult to obtain with other preparation methods and analytical techniques. A novel approach for the preparation and measurement of mineral particles in cross-section was investigated in this work. The unique sample preparation method involves vacuum embedding the mineral particles in epoxy and mechanically fracturing the mineral particles across their lengths. The morphology and characteristics of the particle cross-sections can be directly observed in a FESEM. The dimensions of the particle cross-sections can then be measured from the FESEM images off-line with a commercial software package. The procedure was used to characterize a chrysotile standard reference material, South African crocidolite and an amosite standard reference material. The major and minor cross-section chord lengths were recorded for 25 particles for each of the three samples. The chrysotile sample had average major and minor cross-section chord lengths of 0.06 µm and 0.05 µm, respectively. The South African crocidolite sample had average major and minor cross-section chord lengths of 0.09 µm and 0.07 µm, respectively. The amosite sample had average major and minor cross-section chord lengths of 0.23 µm and 0.15 µm, respectively. The chrysotile sample had the smallest cross-sectional chord measurements, while the amosite had the largest cross-sectional chord measurements. The average chord cross-section ratios of the major to minor chord lengths were 1.1 for chrysotile, 1.4 for crocidolite and 1.7 for amosite. The chord cross-section ratios illustrate that chrysotile has a nearly circular cross-section in comparison to crocidolite and amosite.

Alessandro Pacella, Giovanni B. Andreozzi, Paolo Ballirano and Antonio Gianfagna - Crystal chemical and structural characterization of fibrous tremolite from Ala di Stura (Lanzo Valley, Italy).

Abstract -The present work reports new chemical and structural data of fibrous tremolite from Ala di Stura (Lanzo Vally, Piedmont, Italy). From the toxicological point of view, this fibrous tremolite species exhibited high carcinogenicity in previous intraperitoneal injection experiments with rats. Crystal-chemical data were obtained by electron microprobe and ICP-MS analysis, Mössbauer and FT-IR spectroscopy, and parallel-beam X-ray powder diffraction. Fe2+ occurs at the [M(1)+M(3)] and M(2) sites, and Fe3+ is present only in M(2) site. No evidence of a split M(4) site was observed. The presence of Fe2+ at both M(1) and M(3) sites was confirmed by FT-IR spectroscopy, whit M(1) = 0.09 apfu and M(3) = 0.05 apfu. The cell volume, 909.07(2) Ĺł, is higher than that for the end-member (Ca/Mg= 2/5) tremolite, in accord with the presence of small amount of Fe; the sample has the following formula: Ca_1.96K_0.01Na_0.01)E_1.98(Fe³⁺_0.03Fe²⁺_0.26Mg_4.69Mn_0.03)E_5.01(Si_7.99^IVAl_0.01)E_8.00O₂₂(OH_1,98F_0.02)E_2.00.

Luigi Paoletti, Biagio M. Bruni, Lorenzo Arrizza, Simona Mazziotti-Tagliani and Alessandro Pacella - A micro-analytical SEM-EDS method applied to the quantitative chemical compositions of fibrous amphiboles.

Abstract - In this work, a new micro-analytical SEM-method to perform quantitative chemical analyses of mineral fibers is described. The method makes it possible to correct the EDS results of fiber analyses, obtained by means of the conventional procedure (i.e., ZAF) utilizing, as compositional reference “standards,” small fragments of massive crystals whose composition was previously determined by Electron Microprobe (EMPA). The method reduces the errors in evaluating the chemical composition of fibers due to two principal effects: “absent mass” and “reduced absorption” ” related to the small size of the fibers. The correct quantitative analyses of the fibers were obtained on the base of: a) the trends (i.e., regression equations) of the element concentrations in the “standard fragments” ” (as obtained by ZAF correction) versus the fragment sizes; b) the setting of correction factors through the ratio between the true element concentrations (as determined by EPMA in the massive crystal) and the apparent element concentrations revealed by the regression equations; and c) the evaluation of the correction factor errors through the residual dispersions (standard deviation s) around the curves. The method was applied for the first time on the fluoro-edenite amphibole fibers found in Biancavilla area, to obtain quantitative chemical analyses. The unequivocal chemical characterization of this fibrous material is extremely important to verify their effective toxicity in environmental and health issues. The micro-analytical method was also applied to fibers of fluor-richterite amphibole to confirm its validity on fibers with higher compositional variability.

Jennifer M. Bellamy and Mickey E. Gunter - Morphological characterization of Libby “six-mix” amphiboles used in in vivo studies.

Abstract - Shape and morphology were determined for 1,200 amphibole particles with width greater than 1 µm by use of the polarized light microscope (PLM) and for 1,200 particles with width less than 1 µm with a field emission electron microscope (FESEM). Also, for each particle the microscopist judged if the particle was a fiber or fragment based on its morphology. The amphiboles characterized herein were used in an in vivo experiment and are the so-called “Libby six-mix amphiboles”: a mixture of six different samples collected by the USGS at the former Libby vermiculite mine site. For the particles greater than 1 µm they were determined to be 35% fibers, 46 % fragments, and 20% “not classified” (i.e., these particles could not with certainty be assigned to either class). For the particles less than 1 µm they were determined to be 34% fibers, 55% fragments, and 11% “not classified.” However, if the aspect ratio, which is commonly used as a counting criteria to distinguish fibers from fragments is used, over 99% of the particles would be considers fibers. These results are in good agreement with an earlier study we conducted on a separate set of Libby amphibole samples.