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National Bureau of Standards Special Publication 506. Proceedings of the Workshop on Asbestos: Definitions and Measurement Methods held at NBS, Gaithersburg, MD, July 18-20, 1977. (Issued November 1978) SELECTION AND CHARACTERIZATION OF FIBROUS AND NONFIBROUS AMPHIBDLES FOR ANALYTICAL METHODS DEVELOPMENT J. C. Haartz and B. A. Lange U.S. Department of Health, Education, and Welfare Public Health Service, Center for Disease Control National Institute for Occupational Safety and Health 4676 Columbia Parkway, Cincinnati, Ohio 45226 and R. G. Draftz and R. F. Scholl IIT Research Institute (IITRI) 10 West 35th Street Chicago, Illinois 60616 Abstract More than 50 mineral specimens of fibrous and prismatic (nonfibrous) amphibole species, including tremolite, grunerite, and cummingtonite, were collected and characterized to determine their suitability for use as reference materials in the development of analytical methods. These methods will be used for the detection and measurement of hazardous materials which are found as workplace contaminants. The specimens have been characterized using light microscopy, x-ray diffraction (XRD), and differential thermal analysis (DTA). Some of these specimens have been purified by appropriate physical or chemical techniques and then ground to provide a material with a mass median particle size of less than 10 Nm (major) diameter. The results of characterization studies of the minerals, including a comparison of the properties determined for each of the specimens, are presented. Differences in physical properties of the fibrous and prismatic tremolite specimens are indicated by the data obtained from OTA and XRD studies. While the prepared quantity of each mineral is quite limited, the source of each of the specimen materials and the appropriate methods of sample preparation have been carefully documented should additional quantities be desired. Key Words: Amphibole asbestos; cummingtonite; grunerite; thermal analysis; tremolite; x-ray diffraction. Introduction= Under the provisions of the Federal Occupational Safety and Health Act of 1970 (PL 91-596), the National Institute for Occupational Safety and Health (NIOSH) is charged with the responsibility for research related to occupational health, including the develop- ment and evaluation of analytical methods for the determination of hazardous workplace contaminants. To meet this charge, the Measurements Research Branch of NIOSH has a program concerned with the development of new analytical methods as well as with the iMention of product or trace names does not constitute endorsement by the Public Health Service. 295 2063105089

evaluation and improvement of existing methods. Many mineral dusts, such as those of the silica polymorphs, talc, and asbestos minerals, are included in the hazardous materials for which analytical methods are needed. Earlier work in the NIOSH laboratory showed that it was feasible to quantitatively determine by x-raydiffraction techniques (XRD) chryso- tile, amosite, and crocidolite using either samples of the bulk material or of airborne dust collected on filters [1]2. However, further work rather graphically demonstrated the fact that specimens of a mineral originating from different deposits often exhibit signif- icant variations in impurity content and crystallinity [2], and consequently also exhibit vast differences in their response to analytical measurement techniques. It was obvious that reference materials were needed for the development of analytical methods, that these materials should be from natural sources, and that they be selected on the basis of purity, especially as to an absence of other similar minerals. Pure minerals could then be mixed with other materials to simulate the mixtures found in samples collected from occupational environments. For asbestos, the International Union Against Cancer (UICC) Standard Reference Samples [3] are available as reference materials for chrysotile, amosite, anthophyllite, and crocidolite. These samples have been well characterized with respect to overall chemical composition (elemental weight o/o) and fiber length distribution [4]. There are also some data relating to sample response to heat treatment, and the electron and x-ray diffraction properties [4,5]. However, since these materials were collected and prepared to provide reference samples for inhalation and injection experiments, they were chosen not for phase purity but to be representative of the various types of asbestos used by industry. Further, the UICC samples do not include specimens of the prismatic (nonfibrous) forms of the minerals. . Other reference materials were also needed by NIOSH for the methods development and evaluation program. Consequently, an effort to collect and characterize at least four representative specimens of each of eighteen minerals from different geographical locations was initiated. Table 1 lists the minerals sought and the techniques used for preliminary characterization of the samples. Following the preliminary evaluation and characterization of these samples, the "best" source specimens were chosen for beneficiation, grinding to a respirable size range, and for further characterization and analysis for impurities. A one kilogram quantity of the ground material was established as the final, processed amount to be prepared of each mineral. It was expected that this amount would suffice as reference material for NIOSH analytical research; the source of selected specimens and the appropriate methods for sample preparation were carefully documented should additional quantities be desired. The following discussion will cover the selection, preliminary separation techniques, beneficiation, grinding, and characterization of some of the amphibole species. Details concerning the other minerals will be published separately. Selection of Minerals More than 80 sources were contacted to obtain the approximately 50 samples of mineral specimens containing amphiboles which were received and inspected. Of these samples, 12 were discarded based on macroscopic examination; 38 were carried through the preliminary characterization steps prior to the final selection of the eleven "best" amphibole samples. Since the final quantity of each mineral needed was large (one kilogram), speci- mens were chosen based on (1) the least contamination by other minerals and the contrast- ing habit, and, (2) the amenability of the specimen to beneficiation for removal of contaminant phases. ZFigures in brackets indicate the literature references at the end of this paper. 296

C3 Table 1. Reference materials sought. Mineral Characterization Techniques Silica -Quartz -Cristobalite -Tridymite X-ray Diffraction Beryl Infra-red Spectroscopy Bunsenite (Ni0) Thermal Analysis Fluorite (TG and DTA) Talc Fibrous Serpentine -Chrysotiie Platy Serpentine -Antigorite Fibrous Amphiboles -Crocidolite Macroscopic Habit -Grunerite ("Amosite") Light Microscopy -Anthophyllite X-ray Diffraction -Tremolite Thermal Analysis Prismatic Amphiboles -Riebeckite -Grunerite -Cunmingtonite -Anthophyllite -Tremalite N O 297 °i w .+ 0 (A 0 e .,

'3` After a macroscopic inspection of the specimens as received, using a hand magnifier, portions were hand ground in an agate or diamonite mortar and pestle. The ground samples were dry sieved to pass, a_325 mesh screen and were further characterized using polarized light microscopy, qualitative x-ray diffraction (XRD), and qualitative differential thermal analysis (OTA). The types and quantities of impurities were noted for each of the specimens, and careful scrutiny was given to the mineral morphology, especially for the samples needed for the fibrous and prismatic (or nonfibrous) habits. For macroscopic specimens, the mineralogical criteria distinguishing the fibrous from the prismatic habit are unequivocal. This is illustrated by the samples of tremolite which are shown in figures 1 through 4. The origin of the fibrous tremolite shown in figure 1 is Alaska, while that of figure 2 is a small sample from Italy which was collected in approximately 1890 and has since been in the collection of the Field Museum of Natural History in Chicago, IL. It was not possible to locate a contemporary source of fibrous tremolite in Italy. The prismatic tremolite in figure 3 is from South Dakota and is a fairly pure sample with an acicular radiated structure which is quite evident in the hand specimens. The sample shown in figure 4 contains interlaced prismatic tremolite, talc and other impurities. Although the individual tremolite "needles" are colorless, the sample has a lavender color which may be due to manganese substitutions [G]. Figure 1. Fibrous tremolite: Alaska, 1X. Figure 2. Fibrous tremolite: Tuscany, Italy, 1X. 298

Figure 3. Prismatic tremolite with calcite: South Dakota, 0.57X. Figure 4. Prismatic tremolite with talc and other impurities, 0.5X. Distinguishing between the fibrous and prismatic habits is less straightforward with microscopic specimens. The photomicrographs of tremolite (figures 5 and 6) illustrate the appearance of fibrous and prismatic tremolite specimens ground to a mean particle size of 3.1 pm and 1.7 pm respectively. Similarities in particle shape are evident, although the mean aspect ratio of the fibrous tremolite particles is greater than that of the cleavage fragments of the prismatic material. 299 2063105093

Figure 5. Fibrous tremolite: Rajasthan State, India, 407X. Figure 6. Prismatic tremolite: Gouverneur, New York, 407X. Table 2 lists the amphiboles, and their sources, which were chosen for any necessary beneficiation and final grinding. The impurities listed are those contaminants determined by microscopic analysis of the hand-separated portions of the desired phase. Some of the amphiboles, including the samples of prismatic and fibrous tremolite as well as crocidolite, were obtained as nearly pure, single phase specimens. Others, such as the prismatic grunerite, anthophyllite, and cummingtonite were intermixed with accessory minerals. Hand specimens of the amphiboles selected for preparation as reference materials are illustrated in figures 7-14. 8 00 a w r+ 0 ~ 0 e A

C 03 Table 2. Aophibole sources. Mineral Geographical Origin Representative Impurities Tremolite Fibrous Udaipur District Plant fragments Rajasthan, India (carbonaceous) & other minerals, <3% Prismatic Gouverneur, N.Y. Talc, Limestone, Hematite, <2X Cummingtonite Homestake Mine, Calcite, Quartz, Lead, So. Dakota other minerals, %30% Grunerite Fibrous Lydenburg District Magnetite & other ("Amosite") Transvaal, South Africa minerals, <11% Prismatic Luce #1 Mine Quartz, Magnetite, Newfoundland other minerals, ~50% Anthophyllite Fibrous Bozeman, Montana Magnetite, Calcite & other minerals, <11% Prismatic 8amble, Norway Quartz, Mica, Rutile, Magnetite, other minerals, +25% Crocidolite South Africa Phases which are too fine to identify, <2% Riebeckite St. Peter's Dome Quartz, feldspar, iron El Paso County, Colorado oxide, and other minerals, ~15% 301

CIS Figure 7. Fibrous tremolite: Rajasthan State, India, IX. Figure 8. Prismatic cumningtonite with associated minerals: Homestake Mine, Lead, South Dakota, O.8X. 302

a. I Figure 9. Fibraus grunerite ("Amosite"): Lydenburg District, Transvaal, South Africa, 0.8X. Figure 10. Prismatic grunerite with quartz: Luce No. 1 Mine, Newfoundland, O.SX. 303

COS Figure 11. Fibrous anthophyllite: Bozeman, Montana, IX. Figure 12. Prismatic anthophyllite with quartz: Bamble. Norway, 0.8X. 04 N O W ~. 0 w 0 b OC