By Damien Knight
Asbestos has become a common household name. Its hazards a concern blared across our TVs during lawsuit commercials. We all have heard of it, but what is it? Why was it mined? To understand asbestos, we first must define it. Here we will describe the minerals defined, talk about its use, mining, and health effects.
The problem with asbestos is its definition. According to Amphibole asbestos soil contamination in the U.S.A., “there are 46 different definitions of asbestos included in Lower’s and Meeker’s (2002) Tabulation of Asbestos related Terminology,” (Thompson, Gunter, & Wilson, 2011, p.690-691). In the TV ads the asbestos referred to is defined in commercial and industry terms. Asbestos is not a mineralogical term. Instead, it is a regulation term to describe “silicate minerals that form bundles of long, very thin mineral fibers,” (Van Gosen, 2007, p. 55). These fibers are defined by an aspect ratio of 3:1 or more. The issue with defining asbestos fibers based on this counting is that many minerals cleave in this fashion. The courts and industry have stated that asbestos, therefore, is “an elongated mineral” (Gunter, 2009, p. 141) and “a fibrous non-combustible compound that can be composed of several substances, typically including magnesium,” (Gunter, 2009, p. 141).
In mineralogical context it is not asbestos we define but minerals with asbestiforms. These “asbestiforms” all have a fibrous habit that is strong and flexible. They are more specifically defined as “a flexible mineral fiber easily separable and arranged parallel to other fibers (Guthrie and Mossman,1993),” (Thompson, Gunter & Wilson, 2011, p. 691). Asbestos then is defined “as the asbestiform variety of several specific, naturally occurring hydrated silicate minerals,” (Van Gosen, 2007). The minerals that make up asbestos are the serpentine mineral chrysotile and several asbestiforms of the amphibole minerals.
Why was asbestos mined to begin with? People mined asbestos due to its physical properties. The fibers are soft like fabric and can be spun into yarn or made into felts. Asbestos is also non-combustible this makes them useful as a fireproofing and insulation material. “By 1958, asbestos was used in about 3,000 applications (Quebec Asbestos Information Service, 1959). By this time, asbestos was being honored for its ‘service to humanity,” (Virta, 2003). Its fibers are versatile Their main commercial properties were insulation, reinforcement, inflammability, absorption, and friction. Asbestos was divided into classes of product based on the above properties. Asbestos was used in asbestos cements, wall paints, pipes, insulation, and many other products. Due to health concerns some products are no longer used, such as asbestos roofing or loose asbestos sprays. The main asbestos products today are asbestos rubber and cements. “The historical lack of substitutes and the technological benefits of asbestos were just a few of the reasons why the industry was established and thrived,” (Virta, 2003). Most asbestos in use today is chrysotile.
Actual mining of asbestos is no longer done in the U.S. the last mine closed in 2002. Asbestos is still mined in some other countries. Mining of asbestos was usually done in open pits with bench drilling.
The serpentine asbestiform is chrysotile. This asbestiform is soluble in lung fluid and considered safe remaining in lung fluid for up to nine months. “Approximately 95% of asbestos used commercially is chrysotile,” (Klein, 2008). The asbestos used in most buildings is chrysotile. Chrysotile’s chemical formula is Mg3Si2O5(OH) 4. It is both greasy and silky, with a fibrous habit and a hardness between 3 and 5. Chrysotile can be orthorhombic or monoclinic with soft fibers and some solid solution. The fibers are hallowed straw like fibers when handled are soft to touch.. Chrysotile with a hardness of 3 to 5 and a specific gravity between 2.5 and 2.6.
Chrysotile is still mined in Russia and Canada, while all mining has ceased in the U.S. Russia is the lead producer of chrysotile with “more than half the world’s production,”(Klein, 2008). The mining of chrysotile is done using dry-milling. Ore is crushed then dried and crushed again to be extracted.
The other asbestos minerals are the asbestiforms of the amphiboles group. These minerals exhibit solid solution and are more needle-like than chrysotile. They comprise of riebeckite in the form of crocidolite, grunerite in the form of amosite, anthophyllite, tremolite, and actinolite. Of the 5 amphiboles, crocidolite (blue asbestos,) and amosite (brown asbestos) are most important. These five amphibole minerals are harder than the chrysotile. They have smooth, less flexible fibers that are thicker and more needle-like. It is these asbestiform minerals that are more dangerous due to being less soluble in lung fluids. 5% of all asbestos used in the united states is amphibole asbestos.
Crocidolite made around 4% of the worlds asbestos production. Crocidolite is the asbestiform variation of riebeckite. Its chemical formula is Na2Fe32+Fe23+Si8O22(OH) 2. Production in South Africa ceased in 1995. Australia has reserves which have not been mined since 1966. Crocidolite is found with Precambrian banded-iron formations. Oxidised crocidolite is found in quartz used in jewellery as tiger’s eye. Crocidolite is a much higher industrial health risk than chrysotile, and the most cancerous form of asbestos.
Amosite is the asbestiform of grunerite with the trade name of “brown asbestos.” It as with most other amphibole asbestos thought to cause respiratory illness. Its chemical formula is Fe7Si8O22(OH)2. Amosite is very rare and was only mined in South Africa. “Demand for amosite began to decline in the early 1970s, in response to health concerns. Amosite mining ceased around 1992,” (Virta, 2003).
The issue with the term asbestos and asbestiform is that it is not just one mineral. Amphibole asbestiforms are indeed a health hazard but chrysotile is relatively safe. Mining asbestos is where it is most hazardous as they are linked to respiratory disease. Low levels of environmental exposure have proven relatively safe.
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