a survey of fibrosity of fibrous amphiboles larry s. pierce fiberquant analytical services phoenix,...
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A Survey of Fibrosity of Fibrous Amphiboles
Larry S. PierceFiberquant Analytical Services
Phoenix, [email protected]
Asbestiform vs. Non-asbestiform
• mineral habit is a macroscopic property (naked eye, hand loupe or stereoscope)
• microscopic properties (PLM, SEM, TEM) of asbestiform minerals vary
• old timer’s “tremolite asbestos, but brittle” indicates that >100 years ago, it was recognized that all that is asbestiform is not the same
Both are asbestiform actinolite
• 1st is straight at any magnification; shiny clear-white under stereoscope; kind of chunky @100x though fibrous; not much brooming
• 2nd is flexible; dead-white under stereoscope; can hardly be seen @100x; lots of brooming
How to Quantify the Differences
• Average Aspect Ratio• Graph of Aspect Ratio Frequency• Quantitative Fibrosity
Measurement (Chatfield 2010, 2011)
Fibrosity procedure Chatfield (Beard Conference, 2010):• grind sample in mortar & pestle• (fractional extraction)• Suspend & prepare TEM drop mounts• measure L & W ~200 fibers >5 um
long @10,000x• plot aspect ratio vs fiber width using
log/log axes
Index of mineral properties• Fibrosity chart procedure is intuitively
satisfying – each fiber is plotted• No matter how asbestiform/non-
asbestiform, there tend to be at least a few data points outside/inside the 20:1 box
• Good mineral property index – every example seems to be on scale
• Let’s define F.I. = % fibers inside the box• What variation in F.I. is normal? examples
of actinolite, tremolite and anthophyllite
Conclusions
• Asbestiform tremolite, actinolite and anthophyllite present a broad and continuous range of fibrosity index
• Little or no correlation of fibrosity index to chemistry
• Little or no correlation to mean fiber length
• Correlation to mean width • Correlation to mean aspect ratio