U.S. DEPARTMENT OF COMMERCE
National Technical Information Service
PB-274 750
Review and Evaluation of Analytical
Methods for Environmental Studies of
Fibrous Particulate Exposures
National Inst for Occupational Safety & Health, Cincinnati, OH
May 77
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BIBLIOGRAPHIC DATA
HEET
1. Report No.
NIOSH-77-204
I. Title and Subtitle
REVIEW AND EVALUATION OF ANALYTICAL METHODS FOR
ENVIRONMENTAL STUDIES OF FIBROUS PARTICULATE
EXPOSURES
May 1977
7. Author(s)
Ralph D. Zumwalde, and John M. Dement
8. Performing Organization Rept.
No.
'. Performing Organization Name and Address
National Institute for Occupational Safety and Health
4676 Columbia Parkway
Cincinnati, Ohio 45226
10. Project/Task/Work Unit No.
11. Contract/Grant No.
2. Sponsoring Oiganization Name and Address
13. Type of Repoit & Period
Covered
14.
15. Supplementary Notes
16. Abstracts
Sampling and analytical methods which may be used to identify and quantify fibrous
particulates in environmental samples are reviewed and the electron microscopic
methods used by NIOSH are described in detail. The main topics covered include:
optical microscopic methods; differential thermal analysis; X-ray diffraction; mic-
rochemlcal techniques; comparison of transmission and scanning electron microscopy;
methods for fiber sampling and analysis, including sample collection and preparation,
analytical instrumentation,and identification and characterization procedures. Elec-
tron photomicrographs" of many Eibrous minerals are included.
17. Key Words and Document Analysis. 17o. Descriptors
Environmental surveys
Atmosphere contamination control
Dust control
Air pollution
Analyzing
Microscopy
Microanalysis
17k. Identifiers/Open-Ended Terms
Analytical methods
17c. COSAT1 Field/Croup
06/J
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Release unlimited
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REVIEW AND EVALUATION OF ANALYTICAL METHODS FOR
ENVIRONMENTAL STUDIES OF FIBROUS PARTICULATE
EXPOSURES
Ralph D. Zuxrtwalde
John M. Dernent
U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE
Public Health Service
Center for Disease Control
National Institute for Occupational Safety and Health
Division of Surveillance, Hazard Evaluations, and Field Studies
Cincinnati, Ohio 45226
P S.I by Ihe Sup int,ndenI of DOCUm.flIS U S C20..fflmIflt
Pr nI ng Office W.ih ngtor. I) C 20402
May 1977
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DISCLAIMER
Mention of company name or product does not constitute
endorsement by the National Institute for Occupational
Safety and Health.
DHEW (NIOSH) Publication No. 77-204
ii
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ABSTRACT
This report reviews sampling and analytical methods which may be used to
identify and quantify fibrous particulates in environmental samples and
describes in detail the electron microscopic methods used by the National
Institute for Occupational Safety and Health (NIOSH). Electron photo-
micrographs of many fibrous minerals are included.
iii
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ACKNOWLEDGMENT
The authors express sincere appreciation to Dennis Roberts and Robert
Phillips of the Industrial Hygiene Section, Industry-Wide Studies Branch,
Division of Surveillance, Hazard Evaluations, and Field Studies, NIOSH,
for their assistance in producing the electron photomicrographs and other
photographs shown in this paper. Special acknowledgtnent must also be made
for the efforts of Patricia Johnson, who assumed the responsibility for
typing and proofreading.
iv
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CONTENTS
Abstract iii
Acknowledgments iv
Introduction 1
Review of Analytical Techniques for Fibers 3
Optical Microscopic Methods 4
Differential Thermal Analysis 6
X-Ray Diffraction 8
Electron Microscopy 10
Selected Area Electron Diffraction 10
Microchemical (Microprobe) Techniques 12
Comparison of Transmission and Scanning Electron Microscopy 13
Sample Preparation for Electron Microscopy 14
Methods for Fiber Sampling and Analysis 18
Sample Collection 18
Sample Preparation 19
Analytical Instrumentation 27
Identification and characterization Procedures 27
Discussion 33
References 35
Appendix A 38
Examples of Minerals Which May Occur in a Fibrous State 39
References 48
Appendix B 49
Diffraction Patterns and Typical Energy Dispersive X—Ray
Spectra for Selected Fibrous Minerals 50
FIGURES
1 Cutting and Removing Millipore Filter Section for TEM
Sample Preparation 21
2 Petri Dish With Whatinan Filters Used for Fusing Millipore
Filters 22
3 Vacuum Evaporator Assembly for Carbon Coating Fused Millipore
Filters and an Example of Carbon Coated Millipore Filter
Sections 24
4 The Removing and Mounting of a Carbon Coated Sample Preparation
Onto a TEM Grid 25
5 Illustration of Modified Ortiz and Isom Mounting Technique 26
6 Analytical Instrumentation Used for Fiber Studies 28
7 Data Sheet Used for Fiber Analyses 31
TABLES
1 Typical Optical Data for Asbestos 5
2 Dispersion Staining Colors for Asbestos 7
V
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INTRODUCTION
Concern for potential health hazards associated with occupational exposures
to fibrous particulates has spurred much research in this area. In addition to
laboratory toxicity studies, the National Institute for Occupational Safety
and Health (NIOSH) has underway numerous epidemiological studies of occupa-
tional cohorts with exposure to fibrous particulates. A large part of these
efforts involve studies to fully characterize occupational exposures.
This characterization of exposure and the identification of microscopic fibrous
particulates has become an important priority in recent years due to their pre-
sence in the environment and their association with pathogenesis.
Many fibrous particulates are minerals which occur in a fibrous (e.g., acicular,
spiny, needle, tabular, etc.) geological state. Some of these minerals are
selectively mined whereas the majority are contaminants found in commercial
products. Appendix A lists some minerals which are commonly found in a fibrous
state.
With the aid of a transmission electron microscope capable of selected area
electron diffraction and energy dispersive X—ray analysis, it is possible to
identify the various types of fibrous minerals. This identification depends
upon the production of accurate xnicrochexnical data, fiber morphology and
structural characteristics, and interpretation of selected area electron
diffraction patterns. A transmission electron microscope fitted with these
analytical accessories is more versatile than other combinations of electron,
optical, and X-ray analytical equipment. It can display the microchemical
X—ray spectra obtained from the particulate and simultaneously obtain crystal
structure data with selected area electron diffraction.
1
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For studies to assess the potential adverse health effect of these particulates,
an analytical design has been developed that will definitively identify fibrous
particulates and allow concentration determinations in environmental samples.
Particular attention is given to differentiating asbestiforzn and non-asbestiforxn
minerals.
Although a variety of analytical methods have been proposed and used to identify
and quantify fibrous minerals, each has limitations. Available analytical
methods are presented and discussed in this paper along with a detailed de-
scription of a method now being used within NIOSH.
2
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REVIEW OF ANALYTICAL TECHNIQUES FOR FIBERS
Many analytical techniques have been proposed to identify and quantify
fibrous minerals. These techniques include optical and electron microscopy,
microchemical analysis, X-ray diffraction, and differential thermal analysis.
All these have instrumental limitations which depend upon the quantity of
material present, morphology, orientation, and chemical composition of the
sample. Hence, identifying and quantifying any fibrous particulate in air,
water, or tissue are difficult for a variety of reasons:
1) Asbestos and other fibrous minerals are generally present in low
mass quantities even though fiber number concentrations may be high.
2) Many analytical techniques cannot differentiate between fibrous
and nonfibrous mineralogical polymorphs.
3) Nany fibrous minerals present in both water and air samples generally
have physical dimensions below the resolution limits of optical
microscopy.
4) In some instances, environmental conditions to which the fibers have
been subjected and/or the different elemental compositions of geologic
formations may alter elemental composition ratios, making positive
identification by chemical techniques impractical.
5) Identification by morphology is extremely difficult and impractical
for many asbestos and nonasbestos fibrous minerals.
6) The analytical methodology of selected area electron diffraction (SAED)
offers some identification capabilities, but only under ideal conditions.
Difficulties in identification are often due to the improper
orientation of fibers, lack of appropriate mineral standards, and
dissemination of other elements within the fibers.
3
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In addition to the identification and quantification of fibrous minerals in
air, water, and tissue, other factors such as particle size and morphology
should also be determined. The following paragraphs describe analytical
methods which have been used to quantify fibrous minerals in environmental,
tissue, and bulk samples. Although most of this discussion centers on the
asbestos minerals, similar arguments apply to each of the fibrous minerals
listed in Appendix A.
OPTICAL MICROSCOPIC METHODS
Several optical microscopic techniques have been used to identify and
quantify asbestos fibers. In the United States, an optical microscopic
technique for quantitative determinations of asbestos fibers in air is used
to determine compliance with the occupational exposure stadards.(U The method
consists of collecting breathing zone samples over 15-minute to 4-hour periods
on membrane filters (Millipore AA). Samples are analyzed by first dissolving
the membrane filter to make it optically transparent and then counting the fibers
at 400—450X magnification by phase contrast optical microscopy. Asbestos fibers
are defined as those particulates with lengths greater than 5 micrometers (pm)
and a length—to-diameter ratio of 3—to—l or greater. This technique is not
specific for asbestos fibers or any other fiber type. In addition it cannot
detect fibers less than approximately 0.2 pm in diameter.
Petrographic microscopic techniques may be used to identify fibers greater than
approximately 0.2 to 0.3 pm in diameter. Various optical crystallographic
measurements such as refractive index, extinction angles, and sign of elongation
may be measured with the polarizing microscope, and compared with data reported
for standard asbestos reference samples. Typical optical data for selected
asbestos minerals are shown in Table 1. (2)
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‘ -7 ’
= long direction of fiber
Table 1
TYPICAL OPTICAL DATA FOR ASBESTOS
Asbestos Type
- -
Crystal
Syste m
Refractive
Indices
- Extinction
Angles
Sign Of
Elongation
Chrysotile
monoc].inic
1.49—1.57
yAL* = O
+
Anthophyllite
orthorhomribic
1.60-1.66
yAL = 00
+
Amosite
monoclinic
1.66—1.70
yAL = 14—21°
+
crocidolite
monoclinic
1.69—1.71
yAL 3—15°
—
Treniolite
inonoclinic
1.60—1.65
yAL = 10—21°
+
Actinolite
monoc].inic
1.62—1.68
yAL = 10—15°
+
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Dispersion staining used with plane polarized light may also be used to
differentiate between asbestos and other fibers. (2,3) with this technique, the
fibers are immersed in a mounting liquid with a similar refractive index but
a steeper dispersion curve than that of the fibers. A central or annular
stop is used in the back focal plane of the objective lens to allow for
appropriate dispersion colors. When plane polarized light is used, asbestos
fibers show two characteristic dispersion staining colors, one for the light
vibration parallel to the fiber length and another perpendicular to the fiber
length. The dispersion colors depend on the refractive index of the medium
in which the fibers are mounted, as shown in Table 2. Dispersion staining
colors may change slightly depending on the geographic area from which
the asbestos is mined. Fibers less than 0.5 urn in diameter may not be
identified by this technique due to difficulties in distinguishing colors.
DIFFERENTIAL THERMAL ANALYSIS
Differential thermal analysis has been used to a limited extent in determining
asbestos fiber levels in talc samples. Chrysotile (serpentine minerals)
shows a dehydroxylation endotherm at approximately 650°C and an exotherm at
approximately 820°C associated with the formation of forsterite. These peaks
may be used for quantitative analysis. When a 140-mg sample holder with an
exposed loop differential thermocouple and a lO 0 C/rninute heating rate is used,
a 1% level of chrysotile can be detected in pharmaceutical grade talc.
With this method, a dynamic helium atmosphere is maintained to expel gaseous
mineral decomposition products and to prevent oxidation.
6
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Table 2
DISPERSION STAINING COLORS FOR ASBESTOS
USING A CENTRAL STOP AND
PLANE POLARIZED LIGHT
Asbestos Type Refractive Index Dispersion Staining Colors
Liquid Parallel Perpendicular
Chrysotile
1.560
light blue
magenta
Anthophyllite
1.610
blue-green
golden
yellow
Axnosite
1.670
red magenta
golden
yellow
Crocidolite
1.700
magenta
blue magenta
7
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Differential thermal analysis has not been used for environmental samples
because the lower limits of mass detection are extremely poor. In addition,
differential thermal analysis is not capable of differentiating between
fibrous and nonfibrous mineralogical polymorphs.
X-RAY DIFFRACTION
X-ray powder diffractometry is a standard mineralogical technique used in
the analysis of solid crystalline phases. It is also widely used to identify
and quantify asbestos fibers in bulk materials such as talc 5 ’ 61 and other
industrial materials,( 7 ’ 8 ’ 9 ) and to study amphibole asbestos contamination of
water. (10)
X—ray diffraction is generally considered more sensitive for asbestos than
light microscopy but less sensitive than some analytical methods using electron
microscopy. (10) Diffraction lines and relative intensities for each of the asbestos
minerals, as well as other fibrous minerals, have been published and catalogued
in the ASTM Powder Diffraction File. ‘iariations in fiber chemical composition,
especially for the aniphiboles, may result in slight peak shifts from reported
X-ray diffraction data.
Quantitative determinations of asbestos and nonasbestos fiber levels in bulk
samples requires that average particle size be 0.1 to 10 m. A number of
techniques have been used to minimize iireferred orientation including binder
and slurry mounting methods and backloading of dry powders. Rohl and Langer
have developed a m thod for reducing preferred orientation by filtering an
aqueous slurry through Millipore filters using a filtration adapter attached
to a hypodermic syringe. (6) Other investigators have used the backloading
technique with multiple X—ray diffraction scans.
8
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Using conventional X-ray diffraction scan rates (0.5 to 1 degree 2 theta
per minute), the lower limits of detection for the asbestos minerals are
approximately S percent. ( 7 ’ 8 Automated step scanning procedures, by which
diagnostic reflections are slowly scanned and integrated counts recorded,
have been reported to significantly increase detectable limits, using the
automated step scanning procedure, the sensitivity for asbestos in talc
has been increased to detect as low as 0.1 percent asbestos when using ex-
ternal dilution standards for calibraticn. (6) Similar lower detectable
levels have been reported by other investigators. ( )
X—ray diffraction has limited application for routine analysis of environmental
samples for asbestos fibers. Birks et al. (11) studied the quantitative analysis
of airborne asbestos by X-ray diffraction. They used a specially-designed
diffraction apparatus housing two X-ray detectors. Their technique involved
alignment of the asbestos fibers in an electrostatic field to enhance diffraction
intensity. A lower detection limit of 0.4 to 0.5 micrograms for chrysotile
was reported. However, this technique has not been applied to actual en-
vironinenthl samples. NIOSH is presently evaluating this technique with
chrysotile collected on silver membrane filters. Preliminary results suggest
a lower limit of detection of 15 micrograms.
Amphibole and cummingtonite-grunerite mass concentrations in water samples
have been semiquantitatively determined using X—ray diffraction with step
scanning.(1O) This technique requires filtering the water through 0.45 micro-
meter Millipore filters followed by step scanning a major amphibole dif-
fraction peak (110) and a peak specific to cummingtonite-grunerite (310).
The integrated peak count above background is recorded with mass concentratsons
determined using external dilution standards.
9
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The proper selection of diagnostic i eflections to maximize detection sen-
sitivity and minimize interference due to other mineral phases is necessary
for the best use of X-ray diffraction. It must also be recognized that
X—ray diffraction methods, like differential thermal analysis, cannot dis-
tinguish between fibrous and nonfibrous mineralogical polyrnorphs.
ELECTRON MICROSCOPY
Both transmission and scanning electron microscopy have been used to identify
and quantify particulates. Data from morphological observation, analytical
data from selected area electron diffraction, and rnicrochemical analytical
techniques may be used to identify particulates.
Selected Area Electron Diffraction
Since all crystalline materials scatter electrons in regular patterns relative
to their crystal structure, a transmission electron microscope (TEM) with
selected area electron diffraction (SAED) may be used to form a diffraction
image on the electron microscope viewing screen. The diffraction image of the
scattered electrons can be predicted by Bragg’s Law. Observation of single
fiber (single crystal) electron diffraction patterns may be used to dif-
ferentiate chrysotile fibers from amphibole fibers.(l21 The SAED pattern
for any chrysotile fiber tends to be analogous to a rotating or oscillating
crystal X-ray diffraction pattern in which the long dimension of the fiber
tends to lie nearly parallel to the supporting membrane and therefore per-
pendicular to the incident beam. Chrysotile fibers usually produce streaked
diffraction patterns (due to lattice defects) with the streaks or layer lines
perpendicular to the fiber length. The spacing between the layer lines denotes
the fiber ‘a” axis of approximately 5.3 angstroms. 10 ) The reflections along
10
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the layer lines are usually very streaked and Debye—Scherrer rings may be
observed when clumps of randomly oriented fibers are presented. Progressive
electron-beam bombardment may, however, alter the diffraction pattern due to
fiber damage. (10)
Chrysoti].e fibers can appear as bundles of fibrils or round single fibrils.
Often, the fibrils can be distinguished by their tubular appearance. This
tubular appearance is characteristic of chrysotile, but is not always dis-
cernible due to beam damage 2 or the attachment of amorphous material. (14)
Chrysotile and other fibrous minerals, such as halloysite, have hollow centers.
The amphibole minerals are generally straighter in physical appearance than
chrysotile fibers. Observation of ainphiboles using transmission electron
microscopy often reveals light and dark banding (diffraction images) which
may cross the fiber at right angles. (12) Since the selected area electron
diffraction patterns for all the amphibole asbestos minerals are similar,
observation of these patterns may only identify the fiber as being a fibrous
ainphibole. ( 10 s 12 ) Amphibole electron diffraction patterns show layers and
sometimes streaks perpendicular to the fiber length with the spacing between
the layer lines or streaks representing the fiber “c’ axis of approximately
5.3 angstroms. There is less streaking along the layer lines, in contrast
to chrysotile, with the spot repeat along the lines representing one of the
two remaining lattice spacings (“b” or “a”), depending on fiber orientation
relative to the electron beam.
In addition to observation of electron diffraction patterns for fiber identif i—
cation, photoxnicrographs can be made of the diffraction patterns and crystal “d”
11
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spacings measured from the plate and calculated, using the instrument
camera constant. 3 Both “spot” and polycrystalline patterns may be
measured; however, these intensities may not be,the same as those ob-
served for X—ray powder patterns. Additional reflections may be present,
and measurements of “d” spacings are less accurate when electron diffraction
is used than when X—ray diffraction is used.
Microchemical (Microprobe) Techniques,
Electron beam microchemical analysis may ‘someti ies Ibe used to distinguish
asbestos fibers from other fibrous particles. 5 ’ ’ 17 ’ 18 ) The most
common system in use is the energy dispersive X—ray detector in combination
with either a scanning or transmission electron microscope. Wavelength X—ray
analyzers and the conventional electron microprobe have been used; however,
their routine application is limited due to longer data acquisition times. (18)
Data acquisition times with energy dispersive analyzers, however, are far
less, ranging from 20 to 80 seconds per analysis depending on fiber density,
size, and desired statistical confidence.
Semiquantitative microcheinical analysis with the electron microscope is per-
formed with a beam of high energy electrons incident upon a fiber which
generates X-rays characteristic of the elements in that fiber. These X-rays
are detected by a lithium-drifted silicon crystal detector placed in the
electron microscope column close to the specimen.
The energy of the X-ray photon is converted to a voltage pulse which is
amplified, digitized, stored in a multichannel analyzer or a minicomputer,
and can be displayed on a cathode ray tube. tJ ing the energy dispersive
detector, all elements with atomic numbers of sodium (2=11) or higher may be
analyzed.
12
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Each of the asbestos minerals has a characteristic X—ray spectrum, which,
when combined with fiber morphology, allows for its identification. (15,16,19)
Observation of the semiquantitative fiber X-ray spectrum is usually suf-
ficient for asbestos fiber identification; however, three component dia—
grains have been used after subtracting the continuous background from the
semiquantitative X—ray spectrum. 15 } For asbestos fiber analysis, matrix
corrections are rarely used. Typically iron, magnesium, and silicon are
plotted on the three component diagram and compositional boundaries for the
asbestos minerals established. Unfortunately, this technique suffers from
the inability to use all compositional data obtained, such as the presence
cr absence of sodium, calcium, alu minum, and manganese which aid in the
identification. (12)
With energy dispersive X-ray techniques, the comparison of only elemental
intensities may not be sufficient for positive identification between asbestos
and nonasbestos fibrous minerals which show similar elemental intensities. (14)
For example, chrysotile, anthophyllite, and fibrous talc, all of which have
similar elemental compositions, may be difficult to differentiate. (15,19)
However, these materials may easily be distinguished when elemental data is
supplemented with selected area electron diffraction.
COMPARISON OF TRANSMISSION AND SCANNING ELECTRON MICROSCOPY
Roth transmission and scanning electron microscopy offer certain advantages.
Scanning electron microscopy, using either secondary or backscattered electron
images, offers better observation of surface topography whereas transmission
electron microscopy offers far superior image resolution. Fiber identification
by scanning electron microscopy is limited since electron diffraction studies
are not possible. Scanning electron microscopy combined with microchemical
13
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analysis is sufficient for fiber identification only when the mineralogy
of the fiber source is well known.U 4 ) A new application of scanning trans-
mission electron microscopy (STEM) is now being used on a limited scale.
Electron diffraction studies may be possible with some of these instruments;
however, diffraction patterns are much more difficult to achieve than con-
ventional SAED patterns.
A transmission electron microscope is now available which is equipped with
an energy dispersive X-ray detector, allowing simultaneous observation of
morphology, crystal structure, and elemental composition. This method has
been used to study asbestos fibers in environmental and material samples. 0 l9)
This combination of analytical instrumentation greatly increases the prob-
ability of definitive particle or fiber identification. Many researchers
regard this combination as the “state-of-the-art” with regard to particulate
and fiber studies.
SAMPLE PREPARATION FOR ELECTRON MICROSCOPY
Particulate concentrations in environmental and tissue samples have been
analyzed using a variety of electron microscopy sample preparation techniques.
Environmental samples (air and water) are generally collected on cellulose
ester (Millipore, Gelman, etc.) or polycarbonate (Nuclepore) filters by
concentrating the sample by filtration, centrifuging, etc. (10,20)
For SEMI Nuclepore filters are most often used due to their smooth surface
which may be directly coated with an appropriate metal (gold, platinum, etc.)
and analyzed. Millipore filters tend to have a rough surface texture and are
not generally suitable for direct coating for SEM. Also, small fibers or
particles below the filter surface may escape detection. (20)
14
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For TENS the filter substrate must be removed and the particles mounted on
suitable electron microscope grids. A wide variety of mounting techniques
have been used. The two most commonly used methods are the Jaffe Wick 21 ’ 22
and the condensation washing 23 techniques. These techniques offer simplicity
and maintain most of the original particle size distribution on the sample.
However, some investigators have reported particle losses up to 60% with
Millipore filters when using the condensation washing method with rapid filter
dissolution. Losses with the Jaffe Wick method have been reported to be con-
siderable less (‘10%). (24) Particle loss decreases in the condensation
washing method when much slower filter dissolution is used. A modification
of the Jaffe Wick method has been reported to reduce particle loss. (25) The
filter is coated with silicon monoxide or carbon by vacuum evaporation prior
to dissolving the Millipore filter. Likewise, several investigators have
reported minimal particle loss with Nuclepore filters when the filter is
coated with carbon prior to dissolving the filter substrate 0 ’ 17
In addition to the “direct clearing/mounting” techniques mentioned above, a
variety of other techniques have also been used for preparing environmental
samples. Selikoff et a1. ( 26 have used a “rub—out” technique, in which the
Millipore filter is ashed in a low temperature asher to remove organic or
carbonaceous material. The residue is then dispersed on a microscope slide
using a solution of 1% nitrocellulose in amyl acetate. After grinding with
the surface of a watch glass to liberate individual fibers, the sample is dis-
persed evenly between two microscope slides forming a thin film which is trans-
ferred to standard electron microscope grids. With this technique particle
losses averaging 50% and increases in the number of fibers were reported.
15
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For examining asbestos fibers in biological tissue samples, a variety of
preparation techniques may be employed. (26,27,28,29,30,31) Poo1ey 27 has
used a direct transfer method for formalin-fixed tissue. With this method,
diced tissue is first dissolved in a 40% solution of potassium hydroxide, and
a drop of the digested lung residue is then transferred directly to electron
microscope grids prepared with an appropriate support film. Poo1ey 27 has
also developed a technique for preparing standard histological sections in
paraffin. With this technique, a section is deposited on a glass microscope
slide and washed with xylene and alcohol to remove the paraffin. The sections
are then ashed in a muffle furnace at 450° to 500°C for approximately 15 minutes.
The tissue ash plus any associated minerals are then removed from the glass
slide by a replication process using polyvinyl alcohol. After carbor. coating,
the plastic film is removed by a warm distilled water bath and transferred to
an appropriate electron microscope grid.
t.anger et al. (26) have reported a qualitative method for preparing tissue samples
for electron microscopy. The tissue is dissolved in a 40% solution of
potassium hydroxide and separated in a centrifuge. The residue is then dis-
persed in distilled water and pipetted onto forinvar coated 200 mesh electron
microscope grids. Similar techniques have been used by Pontefract and
Cuznminghazn. (32)
Bouffant 31 has also reported a quantitative method for determining asbestos
fiber concentrations in biological materials. This technique first incinerates
the biological material in activated oxygen at 150°C and then attacks the ash
with iN HCl for 18 hours. The residue is filtered through a membrane filter
which has previously been coated with a carbon film. The membrane is then
dissolved, depositi.ng the fibers on the electron microscope grid substrate.
16
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Asbestos fiber levels in environmental samples and biological tissue are
usually expressed as asbestos fibers per unit volume of sample (fibers/rn 3 ,
fibers/liter, fibers/cc, fibers/gm dry lung, etc.). These concentrations
are determined by counting fibers within calibrated areas on the electron
microscope viewing screen or by counting fibers from photomicrographs.
Asbestos fiber concentrations in water samples determined by laboratories
using the same mounting techniques have been reported to vary by a factor
of 2 to 3• (10) Much larger variations have been reported between labora-
tories using different techniques.
Asbestos (chrysotile) mass concentrations in environmental samples have
also been determined using electron ini.croscopy. This is accomplished by
measuring the length and diameter (volume) of each fiber and calculating
mass using the appropriate density. (26) The accuracy of this technique has
nOt been studied in detail.
17
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METHODS FOR FIBER SAMPLING AND ANALYSIS
FOR ELECTRON MICROSCOPIC STUDIES CURRENTLY
USED FOR NIOSH FIELD STUDIES
SAMPLE COLLECTION
Within any environmental parameter (i.e. ambient, industrial, water, etc.)
the collection of a suitable sample which most closely characterizes an
environment is of utmost importance. This sample must retain the contaminant
without changing its physical or chemical characteristics. Sample collection
is as important as sample preparation and analysis.
As previously discussed, there are basically two sampling filters which have
been used in the collection of particulates, the Millipore (cellulose ester)
and the Nuclepore (polycarbonate). Each of these filters is available in a
variety of pore sizes and filter diameters which make them applicable to the
collection of almost any particulate. The surface properties differ between
the two filters due to their composition. The Millipore surface consists of
a matted network of cellulose ester, creating a circuitous air path through
the filter. The collection efficiency is extremely good due to the surface
topography and the tendency for particles to be collected by impact and inter-
ception. Unlike the Mii.lipore, the Nuclepore has a smooth collection surface,
making it advantageous for electron microscopical evaluation since the col-
lected particulates all lie in one plane. Unfortunately, as the particulate
load increases on the filter surface, the pressure drop increases proportion-
ately. This makes it difficult, during field collection, to obtain a sample
of sufficient size for electron microscopy. In addition, redistribution
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and particle loss from the surface of the Nuclepore often occurs during
handling of the filter. Because of the disadvantages in saiTtple retention with
the Nuclepore, the Millipore is preferred by NIOSH for saxnple collection.
SAMPLE PREPARATION
The analytical procedure requires a sanpie preparation that is suitable for
TEM. Like all preparation methods for TEM, the filter substrate must be re-
moved and the sampled material deposited on a suitable electron microscope
grid. This procedure must be gentle so as not to cause redistribution, change
in physical or chemical nature, or loss of the sample. The two most commonly
used preparation methods reported in the literature for both Millipore and
Nuclepore have been the Jaffe Wick 21 ’ 22 and the condensation washing 23 )
techniques. However, these methods do offer some difficulty in the complete
dissolution of the filter as well as substantial particle loss.
The sample preparation method currently being used by NIOSH is a modifica-
tion of a particle transfer technique developed by Ortiz and Isom. (25) The
technique is designed to utilize various Millipore filters (Millipore AA,
HA, GS, and VM) with different pore size diameters. With this technique,
observed particle losses have not been size dependent, with spherical
particle losses not exceeding 10% and fibrous particle loss less than (25)
Sample preparation requires cutting a section of the membrane filter either
with a cork bore (8mm diameter) or a scalpel. The section is removed and placed
19
-------
sample side up on a clean microscope slide. If the circular section from
the cork bore is used, the edges of the section can be fastened to the slide
with a gummed binder ring. Likewise, if a section is removed with a scalpel,
it can be fastened to the slide using narrow strips of transparent tape
(Figure 1). The slide assembly is placed in a petri dish on top of four
Whatinan filters which have been saturated with acetone and covered (Figure 2).
The acetone vapors destroy the znicroporous structure of the filter by slow
dissolution and produce a fused, microscopically smooth surface on the
sampled side of the membrane filter. The extent of filter exposure to the
vapor is important and is controlled by limiting the time that the filter
is kept in the vapor bath. Specific filter fusion and dissolution times
vary with the types of collected particles. Normally 2 to 15 minutes is
sufficient to produce a smooth matrix. If the filter exposure time is too
long, the fusing membrane may flow around and over the collected particulates
and encapsulate them. These encapsulated particles may later be washed away
by the solvent during the subsequent dissolution step. If the vapor exposure
is too short, the surface fusion of the membrane is incomplete and the final
preparation will contain a coarse, grainy background which results from re-
plicating the residual porous filter structure. A 10—minute fusion time has
been found to be generally acceptable when Millipore AA filters are used.
Once the filter section has been fused, the slide assembly is placed in a
vacuum evaporator on a rotary stage, where the sampled side of the filter is
then coated with carbon by conventional techniques. The rotating filter
20
-------
Figure 1. Cutting and removing
Millipor. filter section for
ThM .ample preparation
L
I
I .
21
-------
Figure 2. Petri dish with
Whatman filters used for
fusing Millipore filters
22
-------
is coated heavily with carbon using a carbon tip which measures 5 mm
in length by 1 mm in diameter. The tip of the carbon rod should be per-
pendicular, approximately 10 cm from the center of the filter section.
The continuous carbon film produced adheres directly to the fused membrane
surface and to the collected particulates (Figure 3).
Next, using the petri dish as a reservior, four Whatnan filters are placed in
the base and saturated with acetone. Several blank 200-mesh formvar/carbon-
coated electron microscope (EM) grids are placed right side up on the Whatman
filters. Sections, somewhat larger in size than the grids, are cut from the
coated filter and placed, sample side down , on the EM grid. The sections can
be readily cut out using an appropriate cork bore or scalpel (Figure 4). Care
must be taken to prevent the coated filter section from curling or shriveling
when it is placed on the EM grid. This can be achieved by holding down the edges
of the filter section with tweezers until the acetone solution has made contact.
The acetone saturated Whatinan filters provide a porous platform for the gentle
chemical dissolution of the original membrane filter. The filter matrix is
dissolved, leaving the particulates adhering to the carbon film, which is, in
turn, supported by the EM grids.
saturation of the tThatman filters should be maintained for 8 to 16 hours to
complete total dissolution of the filter. Acetone nay have to be added periodi-
cally due to evaporation. The acetone solution should never permeate above
the surface of the top Whatinan filter.
23
-------
Figure 3. Vacuum evaporator assembly for
carbon coating fused Millipore
filters
I , , ’
4. ’
Figure 3. Carbon Coated Milhipore filter aections
I
C
*1
24
-------
p. .) P.& p .
p... p. 3
)
Figure 4. The removing and mounting of a carbon
coated saDIple preparation onto a TEM grid
25
-------
FUSED FILTER
CELLULOSE
ESTER
FILTER
PARTICLES
FINIIL PREPARATION
Figure 5. Modified ‘Ortiz and 18cm mounting technique
MICROPOROUS
SURFACE
/
ACETONE VAPOR
S 7 CE
2-10 MINUTES
CARBON
‘I’
I,
/
I
CARBON FILM
FILTER DISSOLVED USING
ACETONE VAPOR 8-16 HOURS
WHATMAN FILTERS
(ACETONE SATURATED)
200 MESH
EM GRID
26
-------
ANALYTIC IL INSTRUMENTATION
The analytical system consists of a .JEOL, JEM bOB transmission!
scanning electron microscope equipped with an EDAX energy-dispersive
X—ray spectrometer. The ‘rEM has a side entry specimen stage that can be
tilted + 600 or the specimen rotated 3600. The energy—dispersive X-ray
detector (lithium—drifted silicon crystal) is fitted through a port in the
TEM column parallel to the specimen holder. The specimen-to-detector dis-
tance is approximately 10 mm with the specimen holder tilted 390 degrees
toward the detector for optimum X-ray collection. The X-ray energy from the
specimen is converted to a voltage pulse which is amplified, digitized, and
stored in the multichannel analyzer. The energy—dispersive detector (EDS)
being used is capable of detecting elements with atomic numbers of 1]. (sodium)
or higher and has an actual energy resolution of less than 170 electron volts.
The x-ray detector is collimated such that a spatial resolution for micro-
chemical analysis of better than 0.5 micrometers is realized.
This combination of analytical instrumentation (TEM plus EDS) permits visual
characterization of particulate morphology, simultaneous observation of the
single-fiber SAED pattern, and fiber chemical composition by X-ray micro—
chemical analysis. The analytical instrumentation is pictured in Figure 6.
IDENTIFI CATI ON AND CRARACTERI ZATI ON PROCEDURES
Samples prepared by the method previously described are placed in
the TEM where three basic pieces of data are gathered to identify and
27
-------
Figure 6. Analytical instrumentation
used for fiber studies
28
-------
characterize all fibrous (3 to 1. aspect ratio) particulates. These include:
(1) visual identification of single—fiber electron diffraction patterns,
(2) visual identification of semiquantitative elemental analysis spectra
using X-ray microchemical techniques, and (3) determination of fiber length
and diameter.
To aid in interpretation of collected data and to allow for comparison with
fiber standard8, several operational parameters of the TEM are maintained
constant. These include (1) sample tilt (39°), (2) accelerating voltage
(100,000 electron volts), (3) beam current (100 microaxnps), (4) energy—dis-
persive x—ray detector to specimen distance (10mm), and (5) the electron dif-
fraction camera constant, which is periodically calibrated. Other data re-
corded with each analysis includes screen magnification, average area of the
sample grid opening, and the number of grids and grid openings analyzed.
Prior to the identification and characterization of the sample, the prepared
grid is first scanned to insure even distribution of particulates and to
ascertain the quality and suitability of the sample preparation. A mag-
nification is then selected that will allow observation of most fibers within
the sample and will permit their size determination. Grid openings for
analysis are randomly selected and all fibrous particulates identified in
the following manner.
1. particulatee must have a length-to-width ratio > 3 to 1 to be
identified as a fiber.
2. SA D is performed on the fiber which is classified as follows by
visual observation:
29
-------
a. Positive amphibole diffraction pattern.
b. Positive chrysotile diffraction pattern.
c. Nonasbeetos diffraction pattern (positive for another mineral).
d. M biguous diffraction pattern (does not allow positive identifi-
cation an amphibole, chrysotile, or nonasbestos mineral, and
includes fibers whose SAED is obscured by debris or overlap).
e. No SAED pattern (includes amorphous fibers and fibers too thin
to give an observable SAED).
3. Microchemical analysis is performed on the fiber displaying the
spectrwn on the video display. Background X-ray counts are sub-
tracted, the elemental ratios compared, and an identification
made by visual comparison with known standards.
4. The identified fiber is sized with calibrated circles or millimeter
markings etched on the TEM viewing screen.
5. Selected pictures of microchemical analysis and/or SAED patterns are
taken and stored for reference.
The format used to record the above information is shown in Figure 7.
Fiber concentrations are then calculated using the average grid opening
area as the counting field area. Average grid opening areas are determined
by optical microscopy by measuring randomly selected grid openings. Measure-
ments are performed periodically to assure continuity of grid opening areas.
To optimize statistical accuracy of the analysis while keeping analysis
time to acceptable limits, 10 grid openings or 50 fibers are analyzed
30
-------
Operatin Conditions
Av.
No. of
Mode:
Beam Current pA:
Sample Tilt 0 :
Magnification:
Grid Area, =2:,
Grids Counted:
Fiber
#
Diffraction Pattern
Possible
EDXRA
ID
Fiber Size,
Picture
Taken?
Dia.
Length
Positive
Amphibole
Positive
Chrysotile
Non
Asbestos
Ambiguous
Pattern
No SAED
Pattern
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
.
22
23
24
25
______ ___________ ________ Comments:
n _i__ _. ..,a C__ rlt_
Sample Data
Sample #:_
Study:
Date:
Analyst
Filter Type:
Mounting Tech:_
Total ,
-------
from each sample, with a minimum of 5 grid openings analyzed. Typical
analysis times average 90 minutes to 2 hours per sample.
In order to be as definitive as possible in both the identification of the
SAED and the simultaneous microchemical analysis, bulk quantities of the
sampled minerals, preferably from the same geologic source, should be ob-
tained and also characterized. These bulk minerals can be utilized as ref—
erence standards for both SPIED and inicrochemical analysis. These reference
minerals are often more reliable than UICC standards, since chemical com-
position ratios differ for like minerals due to the association of other
mineral fragments and the leaching of chemical elements during initial for—
ination.
32
-------
DISCUSSION
The addition of X-ray analytical equipment with a standard TEN,
it is possible to obtain semiquantitative chemical analysis of single
fibers, even though they may be submicroscopic in size. The ability to
accumulate microchemical data from a particulate is often dependent upon
the size, angle of detection, and density of the given particulate. The
microchemical analysis of these particulates can be enhanced by operating
at 100 kilovolts, reducing the size of the beam spot for increased spatial
resolution, and adjusting the beam stigxnator to elongate the beam over the
fiber. These procedures allow fibers with diameters as small as 200
angstroms to be effectively analyzed.
Most environmental samples containing fibrous minerals will readily allow
microchemical analysis for 90% to 95% of the observed fibers. The identif i-
cation of fibrous minerals, however, should not be based entirely upon a
visual examination of the X—ray spectra, unless a bulk quantity of the
observed mineral has been characterized for a chemical composition reference
and a substantial number of the fibrous minerals present have been simulta-
neously identified with SAED. This is necessary when characterizing any
sample of unknown and/or mixed fibrous minerals because of observed similar-
ities in chemical compositions of many asbestos and nonasbestos minerals.
Fibrous minerals with similar chemical compositions are illustrated in
Appendix B.
Most researchers agree that the SAED of a fibrous mineral may often be
sufficient for a positive identification as long as measurements of crystal
spacings are performed and compared with a reference. Identification by
33
-------
this methodology may be difficult due to the preferred orientation of the
fiber to the beam and the length of time required to identify a single
fiber. In addition, the identification of observed fibers by SAED very
seldom exceeds 50% to 60% when the sample is collected from water, ambient
air, or industrial environments.
A rate of identification of fibers greater than 50% to 60% can be obtained
if microchemical analysis is utilized along with the SPEED. Positive
identification of additional fibers is possible when both SAED and micro-
chemical analysis are used. Those fibers which do not exhibit a SAED
pattern can be distinguished if the chemical composition determined by micro-
chemical analysis for that fiber is identical to the composition of those
fibers which previously have been identified by both SIED and microchemical
methods. By utilizing both of these analytical methods, a more definitive,
qualitative, and quantitative analysis can be achieved.
34
-------
REFERENCES
1. U.S. Code of Federal Reg .i1ations, Title 29, Part 1910.1001. U.S.
Department of Labor, Occupational Safety and Health Administration,
Occupational Safety and Health Standards.
2. Julian, Y. and McCrone, W.C., Identification of Asbestos Fibers By
Microscopical Dispersion Staining. Microscope 18: 1010, 1970.
3. McCrone, W.C. and Stewart, Ian M., Asbestos, American Laboratory,
April, 1974.
4. Schlez, .3.?. The Detection of chrysotile Asbestos at Low Levels in
Talc by Differential Thermal Analysis. Thermochemica Acta 8: 197-
203, 1974.
5. Stanley, H.D. and Norward, R.E., The Detection and Identification of
Asbestos and Asbestiform Minerals in Talc, Presented at Bureau of
Mines Talc Synposiwn, Washington, D.C., May 8, 1973.
6. Rohl, A.N. and langer, A.M., Identification and Quantitation of
Asbestos in Talc. Env. Health Perap. 9: 95-109, 1974.
7. Crable, J.V. and Knott, M.J., Application of X-ray Diffraction to the
Determination of Chrysotile in Bulk and Settled Dust Samples. Amer.
md. Hyg. J. 27: 383—385, July—August, 1966.
8. Crable, J.V. and Knott, M.J., Quantitative X—ray Diffraction Analysis
of Crocidolite and Amosite in Bulk or Settled Dust Samples.
Amer. md. Hyg. J. 27: 449-453, September-October, 1966.
9. Keenan, R.G. and Lynch, J.R., Techniques for the Detection, Iden-
tification and Analysis of Fibers. Aster. md. Hyg. 3. 31: 587-
597, September-October, 1970.
10. Cook, P.M., Rubin, J.B., Maggiore, C.J. and Nicholson, W.J., X-ray
Diffraction and Electron Beam Analysis of Asbestiform Minerals in
Lake Superior Waters. Proc. Intern. Conf. on Environ. Sensing and
Assessment, Pub. by IEEE, Piscataway, N.J. 1976, 34(2): 1—9.
11. Birks, L.S., Fatemi, M., Gilfrich, J.V. and Johnson, E.T., Quantitative
Analysis of Airborne Asbestos by X—ray Diffraction: Feasibility Study
AD-A007530, Naval Ras. Lab., Washington, D.C., 1975.
12. langer, A.M., Mack]er, A.D. and Pooley, F.D., Electron Microscopical
Investigation of Asbestos Fibers. Env. Health Perep. 9: 63-80, 1974.
35
-------
REFERENCES
13. Timbrell, V. Characteristics of the UICC Standard Reference Samples
of Asbestos. In Proc. mt. Pneu. Conf. Johannesburg, H. Sharpiro,
Ed., Oxford Univ. Press, London, 1970.
14. Ruud, C.O., Barrett, C.S., Russell, P.A. and Clark, R.L., Selected
Area Electron Diffraction and Energy Dispersive X-Ray Analysis for
the Identification of Asbestos Fibers, A Comparison. Micron 7:
115—132, 1976.
15. Rubin, I.B. and Maggiore, C.J., Elemental Analysis of Asbestos Fibers
by Means of Electron Probe Techniques. Env. Health Persp. 9: 81-84,
1974.
16. Ferrell, R.E., Paulson, G.G. and Walker, C.W., Evaluation of an SEM-
EDS Method for Identification of chrysotile. Scanning Electron
Microscopy: 537—546, 1975.
17. Maggiore, C.J. and Rubin, 1.3., Optimization of an SEN X-ray Spectro-
meter System for the Identification and Characterization of Ultra-
microscopic Particles. Scanning Electron Microscopy, Part I: 129—
136, 1973.
18. Langer, A.M., Rubin, I. and Selikoff, I.J., Electron Microprobe
Analysis of Asbestos Bodies. Histochem and Cytochem J. 20: 735-
740, 1975.
19. Dement, J.M., Zumwalde, R.D. and Wallingford, K.M., Asbestos Fiber
Exposures in a Hard Rock Gold Mine. Ann. N.Y. Acad. of Sc. 271: 345—
352, 1975.
20. Nicholson, W.J., Analysis of Amphibole Asbestiform Fibers in Munici-
pal Water Supplies, Env. Health Persp. 9: 165-172, 1974.
21. Jaffe, M.S., Proceedings, Electron Microscope Society of America
Meeting at Toronto, Canada, September, 1948.
22. Jaffe, N.S., Journal of Applied Physics, Vol. 19, No. 12, p. 1191,
December, 1948.
23. Gerou].d, C.H., Journal of Applied Physics, Vol. 18, No. 4, p. 333,
1947.
24. Beaman, D.R. and File, D.M., The Quantitative Determination of Asbestos
Fiber Concentrations. The Dow Chemical Company, unpublished report,
1975.
36
-------
REFERENCES
25. Ortiz, L.W. and Isom, B.L., Transfer Technique for Electron Microscopy
of Membrane Filter Samples. Amer. md. Hyg. Assoc. 7.: 423—425, 1974.
26. Selikoff, I.J., Nicholson, W.J. and Langer, A.M., Asbestos Air Pol-
lution, Arch, Env. Health 25: 1-13, July 1972.
27. Pooley, F.D., Electron Microscope Characteristics of Inhaled chrysotile
Asbestos Fiber. Brit, J. Indust. Med. 29: 146—153, July 1971.
28. Berkley, C., churg, .1., Selikoff, I.J. and Smith, W.E., The Detection
and Localization of Asbestos Fibers in Tissue. In. let mt. Conf.
Bio. Effects of Asbestos, New York. Ann. N.Y. Acad. of Sciences.
132: 48—63, 1965.
29. Berkley, C., Langer, A.M. and Baden, V., Instrumental Analysis of
Inspired Fibrous Pulmonary Particles, Trans. N.Y. Acad. of Sci., 331—349.
30. Fondimer, A. and Desbordes, J., Asbestos Bodies and Fibers in Lung
Tissue. Env. Health Persp. 9: 147—148, 1974.
31. Bouffant, L.L., Investigation and Analysis of Asbestos Fibers and
Accompanying Minerals in Biological Materials. EnV. Health Persp.
9: 149—153, 1974.
32. Pontefract, R.D. and Cuzmninghain, Penetration of Asbestos Fibers Through
the Digestive Tract of Rats. Nature 243: 352-353, 1973.
37
-------
Appendix A
Examples of Minerals Which May
Occur in a Fibrous State
-------
Examples of Minerals Which May
Occur in a Fibrous State
Mineral Formula Detectable Elements
a)
Occurrence
Name(s)
By Energy-Dispersive
X—Ray Analysis
b)
c)
Associated Minerals
Similar Minerals
Serpentine Mg 6 (OH) 8 Si 4 O 10 Mg-Si a) hydrothermally decomposed olivine;
(chrysotile) proxene, amphibole
(Antigorite) b) olivine, tremolite, talc, opal,
pyrope garnierite
C)
Talc Mg 3 (OH) 2 S1 4 0 10 Mg—Si a) alteration of serpentine;
(Steatite) anthophyllite
b) chlorite, serpentine, rnagnetite,
pyrite, dolomite
c) pyrophyllite, kaolinite
Amosite (MgFe) 7 [ OHSi 4 O 11 ] 2 Mg-Si—Fe a) variety of cummingtonite
(Cuxwningtonlte) b)
(Grunerite) c) chrysotile asbestos
Riebeckite Na 2 Fe 3 Fe 2 Na—Si—Fe a) in crystalline schists, yellow
(Crocidolite) 1 tiger eye
(OM,F)Si 4 0 1 2 b
c)
Tremolite Ca 2 Mg 5 (OH,F) 2 Mg—Si-Ca a) in metamorphic limestone s dolomite,
in talc schists
[ 514011] 2 b)
c) chrysotile, pectolite, wollastonite
Actinolite Ca 2 (MgFe) 5 S i 8 O 22 (OH) 2 Mg—Si—Ca-Fe a) in impure limestone or dolomite
b)
c) pyroxeries
-------
Examples of Minerals Which May
Occur in a Fibrous State
(Cont.)
Mineral Formula Detectable Elements
a)
Occurrence
Associated
Minerals
Name(s)
By Energy-Dispersive
X—Ray Analysis
b)
c)
Similar Minerals
Byssolite Ca 2 Mg 5 (OH,F) 2 Mg-Si—Ca a) in metamorphic limestone and
dolomites, in alpine cracks
[ Si 4 0 11 ] 2 b)
c)
Anthophyllite (MgFe) 7 [ 0HS1 4 0 11 ] 2 Mg-Si +Fe a) in crystalline schists, mica
schists, in metamorphic rock
b)
c) chrysotile
. . Hornblende CaNa(MgFe) (A1FeTi) Na-Mg-Al-Si-Ca—Ti-Fe a) in metamorphic & igneous rocks,
in crystalline schists
S 6 O 22 (O,OH) 2 b) biotite, garnet, epidote, magnet te
c) augite, tourmaline
Epsomite Mg [ S0 4 ]7H 2 0 Mg-S a) weathering product in ore deposits,
efflorescent crusts, alteration pro—
(Bitter Salt)
duct of kieserite
b)
c) kieserite
wollastonite Ca 3 [ si 3 0 9 ] Si-Ca a) in contact metamorphic limestone,
(Table Spar) in crystalline schists
b) quartz, garnet, vesuvianite,
pyroxene
c) pectolite, tremolite
NOTE: (+) may or may not be present
-------
Examples of Minerals Which May
Occur in a Fthrous State
(Cont.)
Mineral Formula Detectable Elements
a)
Occurrence
Name(s)
By Energy—Dispersive
X—Ray Analysis
b)
c)
Associated Minerals
Similar Minerals
Pectolite Ca 2 Nal-I [ Si 3 0 9 ] Na—Si—Ca a) in fissures in igneous rocks
b) zeolite, calcite
c) tremolite, wollastonite
Zeolite Na 2 A1 2 Si 3 O 10 2H 2 O Na—Al—Si a) in cavities in igneous rocks,
(Natrolite) in fissurey in granites &
crystalline schists
b) other zeolites, calcite, apophyllite
c) aragonite scolezite, thomsonite,
mesolite, wavellite
Pyrophyllite A 1 2 [ (CH) 2 Si 4 O 10 ] Al—Si a) in quartz veins & ore veins, in
slate clays
b)
c) talc, kaolinite
Stilpnomelan (K,H 2 0) (Fe,Mg,Al) Mg-Al—Si—K-Fe a) in ore veins
1 (OH) Si 0 (H b) pyrite, siderite, limonite
2 4 10’ 2 ‘2 sphalerite, quartz
C)
Anhydrite Ca [ S0 4 ] Ca-S a) in ore veins, in salt deposits
b) halite, gypsum, dolomite
c) cryolite, gypsum, barytes, calcite
Silli.manite A 1 2 (OSiO 4 ] Al—Si a) in crystalline schists, granulites
(Fi.brolite) eclogites, in contact—metamorphic
rocks
b)
c) cyanite
-------
Examples of Minerals Which May
Occur in a Fibrous State
(Cont.)
Mineral Formula Detectable Elements
a)
Occurrence
Name(s)
By Energy—Dispersive
X-Ray Analysis
b)
c)
Associated Minerals
Similar Minerals
Zoisite Ca 2 A 1 2 [ OOHSiO 4 S1 2 O 7 ] Al—Si-Ca a) in crystalline schists &
& metamorphic rocks
Clino—zoisite b) amphibole, garnet, vesuvianite
epidote, quartz
c) tremolite
Epidote Ca 2 (FeA1)Al 2 Al—Si—Ca—Fe a) in fissures & vesicles of basic
& igneous rocks & crystalline schists
Pistacite [ CHS iO 4 SX 2 O 7 ] b) zeolite, calcite, axinite
garnet, cooper, vesuvianite
c) hemimorphite, aragonite, staffelite;
tourmaline, actinolite.
Zeolite NaCa 2 [ A 1 2 (A1Si) Na—Al—Si—Ca a) in vesicles in basic igneous rocks,
in vesuvianite lavas
(Thomsonite) Si 2 O 10 I 2 6H 0 b) other zeolites, analcite, calcite
c) natrolite. prehnite
Palygorskite (MgA1) 2 [ OHSi 4 O 10 ]4H 2 0 Mg—Al—Si a) weathering product of serpentine
(Attapulgite) b) chalcedony, opal, chlorite,
magnesite -
c)
Sepiolite Mg 4 [ (OH) 2 Si 6 O 15 ] Mg—Si a) weathering product of serpentine
(Meerschaum) b) opal, chalcedony, magnesite,
2H 2 0 -f 4H 2 0 chlorite
c)
-------
Examples of Minerals Which May
Occur in a Fibrous State
(Cont.)
Mineral Formula Detectable Elements
a)
Occurrence
Name(s)
By Energy-Dispersive
b)
c)
Associated Minerals
Similar Minerals
Halloysite A1 2 Si 2 O 5 (OH) 4 Al—Si a) weathering product of kaolinite
b) feldspars, other clays
c)
Brucite Mg(OH) 2 Mg a) low temperature in serpentine or
(Nemolite) dolomite metamorphic rocks
b) periclase
c)
Magnesite MgCO 3 Mg a) metasomatic deposits replacing
limestone & dolomite, in
serpentine in talc schists
b)
c) ankerite, calcite, dolomite
Zeolite Ca [ A1SiC]4H0 Al—Si—Ca a) in ore veins, in cavities &
(Laumontite) fissures in eruptive rocks
b) other zeolites, calcite, chlorite
c) feldspars
Aragonite CaCO 3 Ca a) in rock—fissures, in ore deposits
& embedded in sulfur as sinter
Calcite formation
b)
c) calcite, barytes, coelestine,
strontianite, natrolite, topaz,
dolomite
-------
Examples of Minerals Which May
Occur in a Fi.brous State
(Cont.)
Mineral Formula Dectectable Elements a) Occurrence
Name(s) By Energy—Dispersive b) Associated Minerals
X-Ray Analysis c) Similar Minerals
Apjohnite Mn.Al 2 [ SO 4 ) 4 22H 2 0 Mn—Al-S a) in rock as weathering product
of sulphides
b)
c) alunogen
Gypsum CaSO 4 2HO S-Ca a) rocks in salt deposits, weathering
& product of sulphides in sedimentary
Selenite rocks, in ore deposits
b) anhydrite, aragonite, sulphur
c) mica, talc, kaolinite
Valentinite Sb 2 0 3 Sb a) weathering product of antimony
(Antimony Bloom) ores
b) antimonite, galena
c) cerussite
Arsenopyrite FeAsS S—Fe—As a) in ore veins
b) galena, silver
c) lollingite, chloanthite, skutterudite
Lollingite FeAs 2 Fe—As a) in ore veins
(Leucopyrite) b) arsenopyrite
c)
-------
F.icaniples of Minerals Which May
Occur in a Fibrous State
(Cont.)
MLneral Formula Detectable Elements
a)
Occurrance
Name(s)
By Energy—Dispersive
X—Ray Analysis
b)
c)
Associated Minerals
Similar Minerals
Gedrite (MgFe) 6 A1 2 Mg-Al-Si—Fe a) in metamorphic rocks, in
( i(AlSi)Si o crystalline schists, in granites,
11 in ore veins
b)
c) bronzite
Pyroxene Family
1) Diopside CaMg [ Si 2 o 6 ] Mg—Si—Ca a) in magnetite lodes, in fissures
in metamorphic rocks
b) chlorite, hessonite, magnetite,
apatite, biotite
c) clinochiore, augite
2) Violane CaMg(Si 2 0 6 ]+ Mn, Fe Mg-Si—Ca a)
s-Mn, Fe b)
c)
3) Enstatite Mg 2 [ Si 2 0 6 ] Mg—si a) rock constituent in serpentine,
in pegmatic apatite veins
b) apatite, phiogopite, olivine,
bronzite
c) hypersthene
NOTE: (±) may or may not be present
-------
Examples of Minerals Which May
Occur in a Fibrous State
(Cont.)
a)
rock constituent in basic
rocks, in tuffs, lavas & volcanic
ejecta
b)
c) amphibole
5) Hedenbergite
CaFe [ Si 2 0 5 1
Si-Ca-Fe
a) in metamorphic & metasomatic
rocks
b) magnetite, pyrite
c)
Alunogen
Halotrichite
Al 2 [ so 4 ) lSH O
FeAl 2 [ S0 4 ] 4 221120
Al-S
Al-S-Fe
a) consnon in high—soda, low—silica
rocks
b)
c) nepheline, leucite
a) in ore vens. in coal piles, in
clays
b) pyrite melanterite
c) alunite
a) weathering product of pyrites in
ore deposits, in lignites
b)
c) apjohnite
- ‘I . ugite
Mineral Formula Detectable Elements
a)
b)
Occurrence
Associated
Minerals
Name(s)
By Energy-Dispersive
X—Ray Analysis
c)
Similar Minerals
(Ca,Mg,Fe 2 ,Fe 3 ,Ti ,Al) Mg_A1SiCaT1Fe
(SiA1) 2061
6) Acmite-
Aegirite
NaFeS1 2 O 6 Na—Si-Fe
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Examples of Minerals Which May
Occur in a Fibrous State
(Cont .)
Mineral Formula Detectable Elements
a)
Occurrence
Associated
Minerals
Name(s)
By Energy-Dispersive
x-Ray Analysis
b)
c)
Similar Minerals
Celestite SrSO 4 S—Sr a) in sedimentary rocks, in sand-
stone or limestone
b) fluorite, calcite, gypsum,
dolomite, galena, sphalerite
c)
A
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REFERENCES
1. Heinrich, Wm.E., Microscopic Identification of Minerals. McGraw—
Hill Book Company, New York, 1965.
2. Sorreil, C.A., Minerals of the World. Golden Press, New York.
Western Publishing Company, Inc. Racine, Wisconsin, 1973.
3. Bauer, J., Minerals, Rocks and Precious Stones. Octopus Books
Limited, 59 Grosuenor Street, London Wi, 1975.
4. Pough, F., A Field Guide to Rocks and Minerals. Houghton Miff lin
Company, Boston, Mass., Third Edition, 1960.
5. Kerr, P.F., Optical Mineralogy. McGraw-Hill Book Company, New York,
Third Edition, 1959.
48
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Appendix B
Electron Photomicrographa, Selected Area Electron
Diffraction Patterns and Typical Energy Dispersive
X-Ray Spectra for Selected Fibrous Minerals
-------
ACTINOLITE
Photomicrograph
1 micrometer
Selected Area Electron Diffraction
X-Ray Spectr
Mg-Si-Ca—Fe
a
‘1
•6
A
50
-------
ANOSITE
1 micrometer
Photomicrograph
I I
Selected Area Electron Diffraction
X—Ray Spectrum
Mg-Si—Fe
I
51
-------
ANTHOP}IYLLITE
1 micrometer
Photomicrograph
I
Selected Area Electron Diffraction
X—Ray Spectrum
Mg-Si trace Fe
52
-------
Photomicrograph
1 micrometer ,
Selected Area Electron Diffraction
X-Ray Spectrum
Mg—Si trace Fe
ANTIC ORITE
1
, p... .;‘
. .
j.
a
53
-------
ATTAPULGITE
1 micrometer
Photomicrograph
p
Selected Area Electron Diffractioi.
X—Ray Spectrum
Mg—Al—Si trace Fe
S
54
-------
BRUCITE
1 mIcrometer
Photomicrograph
I- I
Selected Area Electron Diffraction
X—Ray Spectrum
Mg
55
-------
CHRYSOTILE
Photomicrograph
1 micrometer i
Selected Area Electron Diffraction
X—Ray Spectrum
Mg—Si
I,
I
56
-------
CROCIDOLITE
444
Photomicrograph
1 micrometer , - ,
Selected Area Electron Diffraction
X—Ray Spectrum
Na—Si—Fe
I
57
-------
GYPSUM
1 micrometer
Pho tomicrograph
I —S
Selected Area Electron Diffraction
X—Ray Spectrum
S—Ca
4’, -.
58
-------
HALLOYSITE
1 micrometer
Photoinicrograph
-.
Selected Area Electron Diffraction
X—Ray Spectrum
Al—Si
L ’
)
•1
59
-------
NATROLITE
1 micrometer
Photomicrograph
Selected Area Electron Diffraction
X-Ray Spectrum
trace Na—Al—Si
A- ]
V
L
60
-------
PYROPHYLLITE
‘p
Photomicrograph
1 micrometer
Selected Area Electron Diffraction
X-Ray Spectrum
Al—Si
61
-------
,c e
I
I
SEPIOLITE
Photosnicrograph
1 mIcrometer
Selected Area Electron Diffraction
X-Ray Spectrum
Mg—Si
62
-------
TALC
1 micrometer
Photomicrograph
I- -I
Selected Area Electron Diffraction
X-Ray Spectrum
Mg-Si
(
10
I
53
-------
THOMSONITE
Photomicrograph
1 micrometer
Selected Area Electron Diffraction
X—Ray Spectrum
Al—Si—Ca trace Fe
LI
.1
/
1
I ,
I’
.11
64
-------
TREMOLITE
jl,L.b.
1 micrometer
Selected Area Electron Diffraction
X—R.iy Spectrum
Mg-Si—Ca
S
Pho tomicrograph
I- 4
65
-------
WOLLASTONITE
:
1 micrometer
Photomicrograph
Selected Area Electron Diffraction
X-Ray Spectrum
Si—Ca
66
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