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GEOLOGY ARTICLE
Asbestos: what's in a name
by MIKE BALDWIN
07.29.06 -- Any of more than a dozen fibrous minerals can be
classified as asbestos. Controversy still brews over which
fibers constitute true asbestos. Two distinct families of the
mineral exists. The asbestos mineral which is most often found
lying beneath American communities contains chrysotile, the
least toxic. All other asbestos minerals are in a family known
as amphibole asbestos. Tremolite falls into the amphibole
asbestos family.
OSHA (Occupational Safety and Health Administration) was the
first agency to regulate asbestos. OSHA's rules, which rigidly
define the mineral by fiber length and width, only covers
chrysolite and five amphiboles, including tremolite. It's not
that these six minerals are the only ones which contain
potential asbestos hazards; rather, these six minerals are the
only ones which were being widely mined and used commercially
when OSHA wrote their asbestos regulations.
Over the years an EPA (Environmental Protection Agency)
definition of asbestos has expanded to include fibers of a
different size or makeup which may be just as toxic as the
OSHA-defined fibers. For instance, asbestos contamination of
the vermiculite mine near Libby, Montana, (where an epidemic
of lung cancers and other respiratory diseases claimed the
lives of 200 and sickened 1,200 others) was initially
attributed to tremolite asbestos.
Further examination of the Libby mine found that only 6
percent of the material contained tremolite. 80 percent of the
contaminating material contained winchite and the remainder
contained richerite. Richerite and winchite are both
chemically similar to asbestos, but are not classified as
asbestos by OSHA standards. However, the health community does
classify them as asbestos, because both have been found to
trigger asbestos diseases. 1
ASBESTOS is a commercial term used for fibrous silicate
minerals. The fibers of asbestos are chemically
inert as well as heat resistant and flexible.
Asbestos then can be different minerals, but most
commonly it is CHRYSOTILE (a variety of
serpentine). Other asbestos minerals are
tremolite, crocidolite and amosite.
2
TREMOLITE mineral occurs as long, bladed crystals which
are often twinned. It also forms as columnar, fibrous,
or plumose aggregates, often radiating, and in massive
granular habits. It is colorless, white, gray, green,
pink or brown. The streak is white. Tremolite is
transparent to translucent; it has a vitrous luster. It
forms a series with actinolite. Tremolite forms in
contact metamorphosed dolomites and serpentinites.
3
SERPENTINITE is a green, metamorphic rock consisting
predominantly of serpentine minerals. Major constituents
are chrysotile and antigorite. Medium constituents may
include olivine, pyroxene, garnets, amphibole, chromite
and magnetite. Calcite is almost always present. Colors
vary from light gray green to green black. Bluish, brown
and reddish tones sometimes occur. In the stone business
serpentinite is usually just called serpentine like the
mineral. Many serpentinites contain ores which are worth
mining or are very closely associated with deposits (ie.
iron, chromium, magnesite, talc and asbestos).
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©2006 Information for this article was compiled by MAGS
member, Mike Baldwin. Photograph of Fibrous Asbestos courtesy
of Glendale Community College, Susan Celestian. Used by
permission. Information used for educational purposes under
the provisions of the "Fair Use Act of 1976".
References:
01 Janet Raloff; What's in a aname? Asbestos definitions can
depend upon whom you consult; Science News; Vol. 170., No. 2;
Science Service; Washington, DC; pg. 27; July 8 2006.
02 Asbestos; Glendale Community College Earth Science
Image Archive; www.gc.maricopa.edu/. ../asbestos.htm. Accessed
29 July 2006.
03 Chris Pellant; Tremolite; Minerals; Eyewitness Handbooks;
Rocks and Minerals; DK Publishing, Inc.; New York, NY; pg 155;
1992.
04 Walter Schumann; Serpentinite; Handbook of Rocks, Minerals
and Gemstones; Harper Collins Publishers; New York, NY; pg
322; 1993.
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