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C V [ 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) MISIDENTIFICATION OF ASBESTOS IN TALC Jerome B. Krause Colorado School of Mines Research Institute Golden, Colorado 80401 and William H. Ashton Johnson & Johnson Raritan, New Jersey 08869 Abstract Both optical microscopy and x-ray diffraction (XRD) are widely used to detect minerals associated with talc. Optical microscopy can determine the morphology of a particle, but cannot always fully identify the specific mineral. Although XRD is an excellent screening technique for the detection of minerals associated with talc, the method can misidentify minerals due to interferences, interpretive errors, and the inability to determine morphology. Methods for reduction or elimination of these problems include special techniques of sample preparation and x-ray diffraction, combined with microscopic examination (both optical and electron). Key Words: Amphiboles; asbestos; chlorite; electron microscopy; fiber; morphology; optical microscopy; x-ray diffraction; talc. Introduction There are many ways to analyze and study any naturally occurring material. The conclusions reached will often vary widely depending on the expertise and specific interest of the investigator. That situation sums up the present status of "asbestos"; it is also the status of minerals which are associated with "asbestos"; and it is becoming the status of other minerals which can be naturally associated with talc. Popular methods of analysis can give the wrong answer - namely that asbestos is present when it certainly is not. That problem (misidentification) is not so much one of limitations of the methods, but rather one of misinterpretation of data, and failure to recognize the mineralogical background required to certify mineral purity,,for example, when analyzing sheet silicates for asbestos. Unfortunately, one main factor is that asbestos has now developed variable definitions, depending on whether the point of view is mineralogical, industrial, medical, or regulatory. The medical definition is most concerned with whether or not the particles are biologically active; the industrial definition is dependent upon flexibility and weavability; the mineralogical definition upon crystallography; and the regulatory definition upon size and aspect ratio. The word "asbestos" stems from ancient Greek and has always referred to a very fibrous industrial mineral product. Since asbestos has historically related to a mineral exploited as an important industrial commodity, we think a combined mineralogical and industrial definition should take precedence [1,2]1. Other presentations during this IFigures in brackets indicate the literature references at the end of this paper. 339 2063105132

I workshop have amply covered the aspects of asbestos terminology, and it is not our intent to provide comprehensive coverage of that subject. Our primary objective is to review some of the basic principles of analysis, and to point out problem areas where identification of "asbestos" has been abused. Analysis Methods and Misidentification of Asbestos It is useful to categorize the various analytical methods which have been applied to talc to highlight inherent principles which lead to misidentifying asbestos as being present. We offer the following general comments on the three principle determinative properties (chemical composition, morphology, structure). Chemical Composition It is well known that every mineral has a specific chemical composition, and that each mineral has an ideal theoretical chemical formula (configuration). Unfortunately, many investigators overlook the fundamental point that chemical composition does not identify a specific mineral. A simple example will bring that point into focus: A pearl, an oyster shell, a slab of marble, a piece of chalk, and the minerals aragonite and calcite are obviously different materials, and . yet each will be identified as calcium carbonate. That is to say, chemical analyses will identify them all as the same substance, where everyone knows that a pearl is not a piece of chalk. The same situation exists in certain phases of asbestos analysis. For example, chrysotile, antigorite, lizardite, sepiolite, chlorite, and talc are all hydrous magnesium silicates. But a Meerschaum pipe (sepiolite) is certainly not chrysotile asbestos in spite of the fact that chemical analysis alone could lead to that misidentification. Accordingly, chemistry alone does not identify a mineral, nor do those sophisticated instrumental methods which are based on chemical principles, such as: Wet Chemical Analysis Classical (gravimetric, volumetric) Instrumental (atomic absorption, flame emission) Microprobe (electron and ion) Emission Spectrograph Mass Spectrograph X-Ray Fluorescence Morphology Although the shape of a mineral particle is one of the key characteristics in the identification of a mineral, shape alone cannot be the sole determinant of a specific mineral species. There are hosts of minerals in different mineral classes whose particles have' the same shape. They exist across the spectrum of all classes of minerals and the possibilities are beyond comprehension. Even if we limit ourselves to minerals which occur in the true fibrous state, we would estimate there are up to 100. There have been instances where nonasbestos particles have been misidentified as chrysotile in talc because shape alone was the index used. Methods based on morphology include: Optical Microscopy Automated Image Analyzers Electron Microscopy (SEM and TEM) 340

Structure The configuration of atoms in the crystal lattice of a mineral does not necessarily determine a mineral species. The atomic arrangement at the molecular level does not always carry through to the external visible physical form. That is to say that methods based on molecular structure can misidentify a mineral. For example, chrysotile asbestos is classified with the sheet silicates because of its crystal structure arrangement, but it certainly does not occur in flat sheets like the micas or its sibling, antigorite. Methods of identification which relate to molecular structure are: Infrared Spectroscopy Differential Thermal Analysis X-ray Diffraction Electron Diffraction In general then, no single property defines a mineral, and no single method which depends on one property can identify a specific mineral. Conversely, methods which depend on a single factor or characteristic of a mineral can give misidentifications. Two Popular Methods Optical microscopy and x-ray diffraction methods require some additional discussion primarily because they have received widespread attention by industry and gpvernment laboratories as possible monitoring techniques. Although both these methods are fundamental to the science of mineralogy and are highly reliable in the hands of experts, complications arise when shortcuts are taken in the professional procedures. Optical Microscopy When an experienced optical mineralogist or crystallographer identifies a mineral with a petrographic microscope, he can come to a remarkably accurate conclusion. The reason for high accuracy is that not one but several specific properties are determined, such as refractive indices, extinction angle, birefringence, and optical orientation. Specific training and wide mineralogical background are required to get the right answer. In contrast, current optical methods in federal regulatory proposals relating to asbestos presume that asbestos is present in the first place. The analyst then merely observes the mineral particle for size/shape. Consequently, those methods which depend solely on aspect ratio give misidentification. They misidentify the presence of asbestos by such simple oversights as looking at a platelet on edge and counting it as an asbesti- form particle. It is not necessary to elaborate on the other shortcomings of those methods in view of the recent NBS report on the analysis of 80 industrial talcs [3] evaluating that methodology. The same shortcomings were also recently corroborated in a study conducted by Harvard University and NIOSH [4]. However, there are a few rare cases where abnormal crystal habit can be misleading and subtly can lead to a misidentification. Optical microscopy is most vulnerable to this type of misidentification. For example, talc normally occurs as micaceous plates, but rare acicular talc does exist, and one must be very careful to avoid misidentifying the rare occurrence as asbestos. As an example, our XRD examination of an industrial acicular talc sample has identified the presence of significant amphibole (probably tremolite). However, when the material was subjected to thorough petrographic examination it was found to be composed of free grains of columnar amphibole and acicular talc and composite talc- amphibole. The significance is that an erroneous conclusion could be reached by misidentifying such a rare talc variety as asbestos, if only aspect ratio and simple optical microscopy were used. 341 2063105134

Thus, simple optical microscopy can determine the morphology of a particle, but if used alone it cannot always fully identify the specific mineral observed. . X-Ray Diffraction Although x-ray diffraction (XRD) is a valuable technique, it cannot determine the physical shape of a mineral particle, and for that reason it cannot determine whether or not a sample is asbestos. Furthermore, it cannot distinguish between two mineral varieties in the same mineral class in cases such as the asbestos minerals and their nonasbestiform analogues. It is surprising that such a basic shortcoming continues to be overlooked by responsible investigators alleging to have identified asbestos by XRD. One result of the inability of powder XRD to differentiate between the asbestiform and nonasbestiform varieties of a mineral is the potential error of prejudging an XRD detected phase to be the asbestiform variety. For example, preparing calibration standards of mixtures of talc plus chrysotile could have the effect of causing a serpentine peak in an unknown sample to be prejudged as the asbestiform variety, i.e., chrysotile. A mixture of talc spiked with the serpentine mineral chrysotile will give the same XRD pattern as a mixture of talc spiked with the very common platy serpentine mineral antigorite. It should be obvious that an unknown talc showing a serpentine peak cannot be pre,7udged or branded as containing chrysotile asbestos under such circumstances. Unfortunately, the literature has articles by responsible authors who have overlooked that error in logic [5,6,7]. For research purposes only, single crystal XRO can provide information as to whether or not the specimen could be asbestos. However, due to the difficulty of handling minute specimens, single crystal XRD is inadequate for particles smaller than about 20 x 5 pm, and, of course, is also inadequate for routine monitoring procedures. Amphiboles Each of the five amphibole minerals, anthophyllite, cummingtonite-grunerite, riebeckite, tremolite, and actinolite has an asbestiform variety, namely anthophyllite asbestos, amosite, crocidolite, tremolite asbestos, and actinolite asbestos, respectively. Tremolite asbestos is quite rare, and actinolite asbestos is so rare that a recent NIOSH project to prepare reference standard minerals has been unable to locate a source of pure actinolite asbestos [8]. The amphiboles (named from the Greek "amphibolos," meaning ambiguous) are characterized by similar crystal structure and wide variation in chemical composition and appearance. All amphiboles have XRD patterns which are similar° and are characterized by having their (110) or (210) diffraction peaks occur within ±0.2A of each other (Table 1, Figure 1). Reliable identification of individual amphibole species is difficult in the absence of confirming composition data. Examination of Table I and Figure 1 illustrates that attempted identification of a specific amphibole on the basis of d plo) or d Q10) has good potential for being in error. For example, selection of Joint Committee on Powder Diffraction Standards (JCPDS) card 13-437 as being definitive of tremolite presents serious problems. Twenty-nine additional JCPDS amphiboles have their (110) or (210) peaks within ±0.1°20 of this tremolite (110) peak at 10.56°20. Identification of an amphibole as tremolite on the basis of a peak at 10.56°20 is obviously an identification with very low reliability. In other words, a peak at that location is not necessarily the mineral tremolite since it could be one of 29 other minerals. 342

Table 1. CS or d(210) peak position, and Pmphibole JCPDS Card No's., d(110) relative intensity. JCPDS card # Aa 29 Cu I Name Z3-118 8.58(1) 10.31 100 prieskaite 10-456 8.550) 10.35 100 richterite 20-734 8.53(1) 10.37 70 mboziite 20-378 8.52(1) 10.38 100 dashkesanite 14-633 8.51( )1 10.39 70 arfvedsonite 21-149 8.51(1) 10.39 55 hornblende 19-467 8.50(1) 10.41 100 ferropargasite, syn 20-982 8.50(1) 10.41 65 richterite, syn 23-665 8.48(1) 10.43 45 richterite, calcian, syn 23-664 8.47(1) 10.44 ' 35 edenite, sodian, syn 23-667 8.47(1 10.44 45 richterite, calcian, syn 23-663 8.46(1 10.46 40 eckermanite, calcian, syn 9-434 8.45(1 10.47 50 hornblende 13-499 8.45 1 10.47 100 ma9nesioriebeckite 20-656 8.45 1 10.47 100 magnesioriebeckite 20-470 8.44 1) 10.48 100 crossite 23-666 8.44(1) 10.48 40 tremolite, sodian, syn 20-469 8.43( )1 10.49 100 hastingsite 23-1405 8.43(1) 10.49 80 edenite 23-1406 8.43( )1 10.49 40 paragasite 20-1310 8.43(1) 10.49 40 tremolite, syn 10-428 8.42(1) 10.51 100 richterite, fluor, syn 23-603 8.42(1) 10.51 100 tirodite 10-431 8.41( )1 10.52 8D edenite, fluor, syn 19-1061 8.40(1) 10.53 100 riebeckite 20-481 8.40 (1) 10.53 100 hornblende 20-1390 ( 8.40 )1 10.53 90 winchite 23-302 ( 8.40 1 10.53 100 cummingtonite, mangoan 19-1063 8.39(1 10.54 70 richterite 13-437 8.38(1 10.56 100 tremolite 17-478 8.38(1 10.56 65 kaersutite 23-495 8.38(1 10.56 80 eckermanite 9-330 8.37(1) 10.57 100 tremolite, fluor, syn 17-750 8.36(1) 10.58 25 richterite, ferrian 20-386 8.35(1) 10.59 40 eckermanite, syn 22-531 8.35(1 10.59 30 joesmithite 16-401 8.33(2 10.62 70 anthophyllite, magnesian, syn 17-725 8.33(1 10.62 100 grunerite 17-745 8.33(1 10.62 100 grunerite 20-376 8.31(1) 10.65 100 crossite 17-726 8.30(1) 10.66 100 cunmingtonite 20-484 8.29(1) 10.67 100 richterite 13-506 8.27(2) 10.70 80 gedrite 23-679 8.27(1) 10.70 90 glaucophane 9-455 8.26(2) 10.71 55 anthophyllite 20-453 8.26(1) 10.71 100 glaucophane 11-253 8.23(2) 10.75 100 ferrogedrite 23-310 8.20(1) 10.79 75 richterite, ferrian 13-401 8.11(2) 10.91 100 holinquistite a (1100)2. Maximum 428(Cu) = 10.91° - 10.31° - 0.6° Table 1 illustrates the very close proximity of the (210) or (110) XRD-peak of all amphiboles, showing the inability to identify a specific amphibole on the basis of d(210) or d(110)' 343

~ so 70 60 RI 50 TREIdOL1TE 20-656 19•1 I 13-437 ~ 13-499 40 ~ ANTXOAryLLITE 20 16•401 9-455 l0 n 40 1001 10.4 10.6 10.6 DEGREES 28 (CuK(C) 10.7 10.9 Figure 1. Anlphibole d(110 or d(210) - peak positions (20 for CuK ) and relative intensity. An additional problem further affecting the reliability of identification by XRD is the effect of shift in peak position caused by slight mispositioning of the sample surface in the instrument. For example, a 100 pn6 mispositioning of the specimen surface will result in a shift of approximately 0.6-0.7 A in d-spacing at low 20 angles [9]. A slight shift in the position of the peak (fro. a different amphibole or mispositioning of the sample surface, for example) could go unnoticed, resulting in misidentification of an amphibole that is not even present. In order to conclusively identify an amphibole by XRO, it is necessary to have an essentially complete diffraction pattern. In order to obtain such an XRD pattern, the sample must have a relatively high amphibole content and the pattern must be acquired with a time-consuming slow scan. Acquisition and interpretation of such patterns is time- consuming, and discourages proper application of the full procedure, especially for routine monitoring where large numbers of samples require analysis. Shortened procedures, such as single peak identification of amphiboles, provide good opportunity for misidentification. The shortened procedure of single peak identification was apparently used in a 1972 paper [7], where our examination of some of the same samples disagreed with 0 ~ identifications of serpentine, tremolite-actinolite anthophyllite, and anhydrite. w 0 344 ~ r+ w a

aa t~? Chlorite-Serpentine Chlorite is one of the most common accessory minerals found associated with talcs. The chlorite group of minerals are somewhat analogous to amphiboles in that they exhibit a wide 'variation in chemical composition and all have a similar crystal structure. The diagnostic Fplor te basal xRD peaks (001), (002), and (004) are characteristic, and occur at about 14A, 7A, and 3.5tt, respectively. As in the case for the amphiboles, specific identification of a particular chlorite species by XRO is difficult. The XRD problem with chloritic talcs is that the serpentine first order basal peak overlaps the chlorite (002) peak, and the corresponding serpentine second order basal peak overlaps the chlorite (004) peak. Generally, however, the chlorite (004) and serpentine second order peaks are separate enough to allow unambiguous determination of the presence of both phases when present in adequate amounts to give definable peaks. Tables 2 and 3 and Figures 2, 3, and 4 are compilations of JCPDS data for the positions of the (004) basal peak for chlorites and (002), (004), or (0012) basal peak for serpentines, respectively. Table 2. Chlorite JCPDS Card No's., d(004) peak positions, and relative intensity. JCPDS , card Y A 2e Cu I Name 10-183 3.60 24.73 100 penninite 20-671 3.60 24.73a 90 k8mmererite 16-351 3.59 24.80 70 chlorite lb 12-185 3.57 24.94 85 kotschubeite 7-160 3.58 24.87 60 kotschubeite 19-749 3.56 25.01 80 clinochlore 7-77 3.558 25.03 50 sheridanite 16-362 3.55 25.08 80 chlorite la 19-751 3.55 25.08 65 sudoite 22-712 3.55 25.08 45 nimite 7-165 3.545 25.12 60 grochauite 7-78 3.541 25.15 60 thuringite 7-171 3.541 25.15 80 diabantite 12-242 3.54 25.16 100 leuchtenbergite 7-76 3.537 25.18 50 ripidolite 13-29 3.53 25.23 80 thuringite 7-166 3.523 25.28 50 daphnite 12-243 3.52 25.30 92 aphrosiderite 21-1227 3.52 25.30 100 thuringite 3-67 3.49 25.52 100 thuringite a d(115)' Table 2 illustrates variation in position of the chlorite d(004) XRD peak. Table 2 should be compared with Table 3 to see that the chlorite and serpentine XRD peaks overlap and interfere with each other. Identification and quantification of serpentine in the presence of chlorite is extremely difficult at best. 345

(oo ~ eo TD 60 50 40 30 20 io 0 4 W A 0 ------ ------------- --~-- - - -- - ---- - - Emm ----------- --- ---- ---- a _. .. _ ___. H0 ----- - _-~ ------_ TO CHLORITE ~ ~ Fi 40 d -.-___ 30 10 i . O a DEGREES 28 (Cu Ka) Figure 2. Chlorite d(004) - peak positions and relative intensity. The data of Table 2 are presented in graphical form showing the variation in position of the d(004) XRD peaks for different chlorites. Selection of JCPDS card 16-362 as diagnostic for chlorite can obviously result in misidentification. 6£TSOI£90Z

cs Table 3. Serpentine, Kaolinite, Halloysite, and Dickite JCPDS Card Nos., peak position, miller index (hkl), and relative intensity. JCPOS Card # , A 2e Cu I hkl 18 -1779 3.67 24.25 80 (002) 9-444 3.66 24.32 100 (0012 21-543 3.65 24.39 70 (004) 7-417 3.63 24.52 300 (102) 11-386 3.62 24.59 60 (002) 21-963 3.61 24.66 80 (002) 12-583 3.56 25.01 80 (0012) 13-4 3.56 25.01 70 (0012) 7-339 3.55 25.08 100 (002) 11-388 3.55 25.08 100 (0012) 7-315 3.52 25.30 100 (002) 9-493 3.52 25.30 100 (004) 6-221 3.58 24.87 100+ (002) 14-164 3.579 24.88 80 (002) 12-447 3.56 25.01 50 (002) 9-453 3.63 24.52 90 (002) 10-446 3.58 24.87 100+ (004) Chlorite 29 Range: 24.73 - 25.52 Serpentines lizardite, 1M antigorite, 60 chrysotile, 2M antigorite, 6M lizardite, 10, aluminian antigorite, 6M antigorite, 60, aluminian antigorite, 60, aluminian berthierine antigorite, 60, syn berthierine amesite Kaolinites kaolinite, 1Md kaolinite, 1T kaolinite, 1T Halloysite halloysite, dehydrated Dickite dickite 2M, Table 3 illustrates variation in position of XRD peaks of serpentine, kaolinite, halloysite, and dickite. The XRD patterns of these minerals interfere with each other and with chlorite (see Table 2). N O ~ W F+ 347 ~ .+ A O

~ SERPENTINE dpapj qp4l.(OOIZ) ®Kl,OLINITE dpp21 ~HALLOYSITE d10m oDICKITE dppsy w P ~ YEGflEES 28 /tuMI Figure 3. Peak positions and relative intensities. The data of Table 3 are presented in graphical form to illustrate the variation in position and interferring overlap of XRD peaks of serpentine, kaolinite, halloysite, and dickite. rrrsorsvoz C4 ,