I was personally interested to see a comment on the statement by Martin S. Rutstein - Doc Rutstein was my mineralogy professor many years ago at SUNY New Paltz where I earned my Bachelor's degree in geology and he's an expert on asbestos having spent a number of decades involved with the science and regulatory aspects of asbestiform minerals (and he led great field trips to Thetford Mines in Quebec).
Those of us with some training in geology will know that "asbestos" is not a scientific term referring to any specific mineral but rather an industrial/regulatory term referring to a group of minerals with specific properties (often not well defined scientifically). In addition, the different minerals which fall into the catagory of "asbestos" do not all pose the same health hazards (how could they, they're all completely different).
Below are three minerals commonly grouped together as asbestos (there are a few others as well). By looking at the formulas, geologists would instantly recognize that blue (riebeckite) and brown (grunerite) asbestos belong to the amphibole group of minerals while white asbestos (chrysotile) is a phyllosilicate from the serpentine group.
Chrysotile - (Mg,Fe)3Si2O5(OH)4 - "White Asbestos"
Riebeckite variety crocidolite - Na2(Fe,Mg)3Fe2Si8O22(OH)2 - "Blue Asbestos"
Grunerite (aka amosite) - Fe7Si8O22(OH)2 - "Brown Asbestos"
There has been a tendency by some to classify all asbestiform minerals as asbestos. Asbestiform is simply a mineralogical term referring to minerals that can be separated into fibers. Many regulatory definitions define a 3:1 length-to-width ratio as a fiber. The problem is that there are many, many minerals which fit this criteria - all with different chemical compositions, atomic structures, and physical properties. If all such minerals were considered dangerous, we're in a lot of trouble since there's no place on Earth we'd be safe from such exposure to these naturally-occuring minerals in many rocks and soils.
That's why most definitions of asbestos describe the asbestiform habit along with a list of minerals that are considered to be asbestos. The EPA, for example, defines asbestos as "asbestiform varieties of: chrysotile (serpentine); crocidolite (riebeckite); amosite (cummingtonite/grunerite); anthophyllite; tremolite; and actinolite." All of these, with the exception of chrysotile, belong to the amphibole group of minerals.
There is consensus that the amphibole asbestos minerals are indeed harmful and pose a risk for diseases like mesothelioma and asbestosis. Chrysotile, however, is another story. Investigating the health hazards of different asbestiform minerals is difficult for a number of reasons:
- Smoking is a huge factor you need to account for since many asbestos miners and workers smoked cigarettes, especially those exposed decades ago when smoking was far more prevelant.
- Often people were exposed to multiple types of asbestiform minerals in mining and processing. Materials like pipe insulation were often composed of different asbestos minerals mixed together as well.
- Many people who worked with asbestos were also exposed to other types of carcinogenic materials.
There is a fair amount of evidence, however, that chrysotile is much less harmful than other forms of amphibole group asbestos minerals. Chrysotile, being a phyllosilicate, has fibers that break down easily in the lungs allowing them to be expelled. Amphibole minerals have much more rigid fibers that stick around to irritate lung tissue. The problem is that asbestos litigation has become a cash cow for rapacious attorneys (the mesothelioma victims get some settlement, but the attorneys become wealthy) and science often takes a back seat when attorneys, politicians, and corporations looking to lessen their liability become involved in issues like this.
On a personal note, I've handled asbestos. All geology students above a certain age handled chrysotile samples in mineralogy lab. I even remember digging some chrysotile samples out of a fault zone on a geology fieldtrip (a sample that sat on my bookshelf for many years). When I started one of my teaching jobs in the late 1990s, I found samples of chrysotile laying around which I placed into sealed containers (by that date, enough was known of the hazards that the previous professor should not have had those laying out for students to handle). I've never heard of high rates of lung diseases among geologists - on most comparisons I've seen, geologists tend to be relatively long-lived (mathematicians and physicists have them beat but chemists, exposed to numerous carcinogens in their careers, have a shorter statistical lifespan).
Anyway, while I don't believe there's a significant risk from handling chrysotile samples, I don't have my geology students handle it for liability reasons. They can examine it in a sealed container. Quite honestly, I'm more worried by the large amount of fiberglass insulation dust I breathed in during my younger days working in construction and as an alarm installer rooting around in attics (and I smoked cigarettes back then too - a far more dangerous exposure to carcinogens). You can drive yourself crazy worrying too much about all the bad things you've been exposed to in life!
Tiger's eye forms when crocidolite asbestos is replaced by quartz fibers