A survey of fibrosity of fibrous amphiboles

A Survey of Fibrosity of Fibrous
Amphiboles
Larry S. Pierce
Fiberquant Analytical Services
Phoenix, AZ



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)
• />(photos/data)