Project for GO 536 Optical Mineralogy
Spring 1998
by
Asbestos is a general term for several naturally occurring fibrous mineral silicates. There are six distinct types of asbestos: actinolite, amosite, anthophyllite, crocidolite, tremolite and chrysotile. Each is different in physical and chemical properties, depending on the other components of the rock, such as calcium, magnesium or iron.
This amosite image is taken from (http://www.uvm.edu/Dept/EHSRM/ASB/asbestos.html).
A Long History:
The first references to asbestos can be traced to several ancient philosophers. One of Aristotle's students, referred to an unnamed substance which resembled "rotten wood" in the book On Stones , written around 300 B.C. The name origin comes from the Greek chrysos-"gold" and tilos-"fiber" GOLDFIBER! In the first century the geographer, Strabo, identified the first Greek asbestos quarry on the island of Evvoia, where fibrous stone threads were combed and spun like wool to make an assortment of flame-resistant cloth items. Throughout time asbestos has gathered many different names, such as: "mountain leather", "incombustible linen, "rock floss" and "feathered alum".
Myths and Legends:
Because of the unique physical properties asbestos has collected many tales of magical powers. During medieval time, alchemists started rumor that asbestos grew as hair on fire-resistant salamanders. A popular legend is that the French Emperor, Charlemagne set an asbestos tablecloth on fire and pulled it out again unharmed to impress some of his dinner guests.
Physical and Optical Properties:
Asbestos has a high thermal stability, excellent tensile strength (stronger than steel), resistance to chemical attack, good thermal and electrical resistance and ability to be subdivided into fine fibers. Perfect lengthwise basal cleavage is a characteristic of asbestos. Hardness can range from 3.5 to 5 , colors: green, gray, bluish gray, brown, black, or white.. And are usually found in metamorphic rocks. Between cross-polarized light it "flashes" meaning it is a anisotropic mineral.
The above images are from a thin section of tremolite under cross-polarized light. These were taken using a petrographic-microscope equipped with a 35mm camera.. Both the images are magnified 100x , notice the fibrous nature in the crystals. The colors that are seen are first or second order of interference figures produced by different wavelengths of light that are refracted slightly at different angles. Photographs taken by C.J.R.
The above image is from a thin section of serpentine under cross-polarized light. It was taken using a petrographic-microscope equipped with a 35mm camera. The photo is taken at a magnification of a 100x. Photographs taken by C.J.R.
The BAD Reputation:
Asbestos fibers can penetrate bodily tissue, particularly the lungs, eventually causing tumors to develop. The largest single source of asbestos in the indoor air we breathe is insulation since it has been used in most of the buildings built in the past 50 years. These fibers do not just become air-born by themselves, usually the renovation or demolition of structures can lead to the release of fibers. "In the year 1973 the use of asbestos was at a all time high, of nearly a million tons" (Alleman & Mossman, 1997, p.7).. It has fallen by about 95 percent sense then. Hopefully chemists / scientists well be able to put these very useful mineral to some good in the future, maybe giving the general public a better feeling of this natural resource.
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References:
Asbestos Revisited, J. E. Alleman & B. T. Mossman, Scientific American July, 1997
http://www.pers-er.com/regs/29cfr/1910/1910_1001_App_J.html
http://www.uvm.edu/Dept/EHSRM/ASB/asbestos.html