A Survey of Fibrosity of Fibrous Amphiboles Larry

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 • 1 st is straight at any magnification; shiny clear-white under stereoscope; kind of chunky @100 x though fibrous; not much brooming • 2 nd is flexible; dead-white under stereoscope; can hardly be seen @100 x; 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, 000 x • 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/johnson 2011. htm (photos/data)