A Survey of Fibrosity of Fibrous Amphiboles

Larry S. PierceFiberquant Analytical Services

Phoenix, AZlspierce@fiberquant.com

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

Fibrosity Chart – very fibrous

Fibrosity Chart – not so fibrous

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

Cast of Characters

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

Moral of the Story

• Instead of referring to an amphibole sample or deposit as merely asbestiform or non-asbestiform, we should rather specify how asbestiform (Fibrosity Index or Confirmed Asbestos or something similar)

• http://www.fiberquant.com/johnson2011.htm (photos/data)