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ANALYSIS OF TALC BY RAY DIFFRACTION AND POLARIZED LIGHT MICROSCOPY
Lucy B. McCrone Walter C. McCrone Associates
Chicago Illinois 60616
Inc.
Contract No. CDC 210-75-0063
U. S. DEPARTMENT OF HEALTH EDUCATION AND WELFARE Public Health Service
Center for Disease Control
National Institute for Occupational Safety and Health Cincinnati Ohio 45226 May 1977
0144772
JNJ 000062312
ERRATA
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The quartz peak at 26.65 is three times the intensity of the next strongest at 20.83 and is preferred except when muscovite mica is present The 26.65 26.65 quartz peak is usually distinguishable by step scanning from the muscovite peak at 26.85 and the biotite mica peak at 26.42 but not from the 25 Intensity muscovite peak at 26.66 When much muscovite is present as in Sample 125
the 20.83 peak is preferable
Minimum levels of detection by step scanning found for standards in talc using the peaks discussed above are tremolite - 0.5 anthophyllite - 2.5 chrysotile - % and quartz -0.2 -0.2 Our tremolite standard is predominantly nonfibrous others have reported that fibrous tremolite gives about 1/4 to 1/3 the response at 8.38^ obtained from nonfibrous tremolite in talc Most of the samples in which we found tremolite contain a preponderance of the nonfibrous habit
POLARIZED LIGHT MICROSCOPY
We have applied two kinds of microscopical analysis in identifying components of talc samples First petrographic observations in plane polarized light mainly
morphology and refractive indices and between crossed polars morphology
birefringence type of extinction extinction angle and sometimes interference figures Second the use of dispersion staining to identify minerals Appendix C the analytical dispersion staining chart is specifically designed for talc samples
Most of the above observations are made at 200X magnification using the 10X
dispersion staining objective with a 20X ocular High power objectives are some-
~
times used to examine the smallest particles and fibers or for interference
figures Our usual procedure is as follows
Procedure
1. Analyze the ray line scan to identify the major components and define any
questions to be answered by microscopy
Lo
2. Mount representative samples about 0.1 mg each of the unmilled material
in the Cargille refractive index liquids specified below Observe central stop dispersion staining colors in each liquid and relate them to the curves in Appendix 3 Check birefringence and extinction between crossed polars and refractive indices relative to the mounting medium Look for fibers by dispersion staining and
between crossed polars and check whether particles are really fibers or plates on edge by making them tumble in the liquid to exhibit all views - tapping on the coverslip with a needle will make the particles tumble into a succession of random orientations Table 2 gives the refractive indices of most minerals of interest in
talc samples
* J. Scheiz private communication |
15
0144774 JNJ 000062314
Table 2. Refractive indices of minerals sought in tale samples
Mineral
Refractive Indices 25
a or w
or
chrysotile
1.544
1.552
1.555
quartz
1.544
1.553
:
lizardite
1.545
-
1.558
)
antigorite
;
1.545
1.557
1.560
'
|
talc
1.546
1.588
1.589
:
chlorite
1.566
1.567
1.596
:
tremolite
1.599
1.610
1.621
:
anthophyllite
1.603
1.617
1.628
:
actinolite
1.633
1.641
1.647
:
forsterite
1.643
1.663
1.682
'
|
calcite
1.653
1.486
:
grunerite amosite
1,669
1.681
1.697
|
dolomite
1.677
1.500
:
magnesite
1.694 1.694
1.509
riebeckite crocidolite
1.698
1.703
1.708
16
0144775 JNJ 000062315
Minerals especially silicates but also the isomorphous series of carbonates calcite dolomite magnesite etc. vary in refractive index Table 2 and
Appendix C show average indices for the minerals which might be found in talc
Generally the dispersion staining curves for these minerals move parallel to themselves as the composition changes The birefringence values ( B and ew ew will generally remain nearly constant for a given mineral although the indices themselves may vary considerably
Both morphology and optics are noted in order to identify the asbestiform minerals To be asbestiform requires that they be fibers as defined by NIOSH
measuring < 5...min diameter 200 min length and have a length to width
ratio of at least 1
Cargille high dispersion liquid D = 1.550
A
representative
sample mounted in this
liquid will show
characteristic
0
colors for any of the following tale quartz chrysotile lizardite antigorite
and many fibers paper silk viscose rayon and human hair etc. The
crystallographic data in Appendix C and morphological observations should ensure
identification of most of these substances or allow the conclusion that any other
substance showing colors in this liquid is not one of those listed Figure 2 Characterization of this extraneous substance will often be possible by referring
to the Particle Atlas
Cargille high dispersion liquid 25 = 1.585
This liquid is useful for distinguishing talc from chlorite Edge views of chlorite
are magenta for the index perpendicular to the plate
index parallel to the plate
ON EDG EDE GE >
Talc is magenta for the
MAGENTA MAGENTA
CHIORITE CHIORITE
vi
lp MAGENTA4 a
MAGENTA4 -
C
=
7.8LC
Cargille high dispersion liquid 25 = 1.605
a
Chrysotile and all other substances giving dispersion staining colors in liquid
1.550 will be white or pale blue in 1.605 Figure 3 Talc is the only substance
in this group that shows a gclose to the visible ca 700 nm All talc plates show both n's "Y ) close to 1.605 in the red hence the central stop shows a pale blue in all directions lying in the talc plate and white corresponding to the a direction Other minerals showing colors in n = 1.605 include tremolite chlorite and actinolite Figure 4
* McCrone W.C. J.G. Delly 1973. The Particle Atlas Edition Two
Ann Arbor Science Publishers Ann Arbor Michigan
17
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JNJ 000062316
Anthophyllite often shows colors similar to tremolite but exhibits parallel extinction on all views Tremolite shows parallel extinction for one view but oblique extinction of 10 to 21 for the a- Y view
Cargille Liquid n = RF series
Non minerals showing dispersion staining colors in n
= 1.660 include
actinolite forsterite hornblende calcite cummingtonite and dolomite Figure 5
Cargille Liquid n = 1.700 M series
in Minerals to look for
and magnesite
My = 1.700 include cummingtonite grunerite crocidolite
t
LIST OF MINERALS .
STANDARDS
The following mineral, standards were used for microscopy and quantitative ray
diffraction
Vermont talc kindly supplied by Windsor Minerals anthophyllite Haddam Connecticut chrysotile Victory Mine Globe Gila County Arizona tremolite Fowler New York
quartz synthetic single crystal
In addition the minerals listed below were used for microscopy and qualitative ray diffraction
lizardite Kennack Cove Cornwall England chlorite Calaveras County California prochlorite Chester Vermont anthophyllite Guffey Colorado . anthophyllite Cashiers North Carolina actinolite Lake Wenatchee Washington tremolite fibrous Dahl Creek Alaska
ray line scans of all of the above are attached as Appendix B.
21
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