A survey of fibrosity of fibrous amphiboles

A Survey of Fibrosity of Fibrous Amphiboles Larry S Pierce Fiberquant Analytical Services Phoenix, AZ lspierce@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) [...]...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... 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) ... normal? examples of actinolite, tremolite and anthophyllite Cast of Characters Conclusions • Asbestiform tremolite, actinolite and anthophyllite present a broad and continuous range of fibrosity. .. “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;... • Average Aspect Ratio • Graph of Aspect Ratio Frequency • Quantitative Fibrosity Measurement (Chatfield 2010, 2011) Fibrosity procedure Chatfield (Beard Conference, 2010): • • • • grind sample