Featured Asbestos – Other Amphiboles

Nov 13, 2019

I’m sure you are familiar with asbestos, but did you know that there are different types of asbestos?  In previous blogs, we discussed the basics of both chrysotile and crocidolite. Chrysotile is a serpentine based mineral which was the most common asbestos used. Crocidolite is a blue amphibole mineral more rarely used than chrysotile. These are just two examples of the six regulated asbestos minerals. Chrysotile is the only regulated asbestos minerals that is serpentine, while the vast majority are amphiboles. Amphiboles are different then serpentine not just by their chemical composition but also their shape. Chrysotile is curly and wavy, while amphiboles are sharp and needle-like. In this blog, we will cover the remaining four amphibole minerals which are amosite, anthophyllite, tremolite, and actinolite.


Amosite is the most common amphibole asbestos mineral found in building materials. For my fellow geology enthusiasts, amosite is the fibrous form of cummingtonite-grunerite (what a mouthful!), which usually forms in metamorphic rock types with higher magnesium concentration. While other asbestos minerals have a more geological name, the root of the word amosite is derived from the company which mined it, Amosa. Amosa stands for Asbestos Mines of South Africa, which is the location where most of the amosite was mined from. While far rarer than Chrysotile, it is estimated to be in 5% of all asbestos-containing materials making it the 2nd most common asbestos variety. In my lab and field experience, amosite is commonly used in varieties of pipe insulation such as magnesia block, some Air Cell pipe insulations, and other thermal system insulations. 


Anthophyllite is a very rare asbestos mineral which was primarily mined from Finland. It is found in less than 1% of asbestos-containing materials. The name is based on a Latin phrase meaning clove due to its similarity in color. It typically forms under metamorphic conditions similarly to amosite. It is so rare that I have only encountered this mineral on two occasions outside of an academic setting. Once in a commercial lab where I discovered it in a sample, the second occasion was throughout an apartment unit. You can read about the second encounter in my previous blog.

Tremolite and Actinolite

Tremolite and actinolite form a solid solution series (last geology phrase I promise). This means the chemical reaction has multiple solutions instead of one. In this case, depending on the amount of magnesium and iron present in the parent rock, either mineral can be created. Like Anthopyhylitte these minerals are rarely seen in asbestos-containing materials. One source that is often seen is a contaminant in vermiculite. Tremolite and other amphiboles such as winchite and richterite (unregulated asbestos) are contaminants found in the Libby, Montana mine where vermiculite was primarily mined. For more information on the Libby amphiboles please look at my previous blog. Outside of an academic setting, I have not yet encountered actinolite in the field. 

The Safety of Chrysotile Vs Amphiboles

Exposure to asbestos fibers may lead to various ailments, however, there is debate over how the type of asbestos may affect one’s health. Some research has shown that the physiochemical makeup of amphiboles is more potent than chrysotile in causing asbestos-related illnesses. One research paper shows that chrysotile may be broken down easier by our immune systems when compared to amphiboles which are more persistent due to their differences. However, the World Health Organization has stated regardless of potency, the scientific evidence is clear that exposure to chrysotile can cause asbestos-related illnesses. 

The take-home point is that all types of asbestos are hazardous. If you have any concerns about asbestos, don’t hesitate to give Indoor Science a call or post a question in the comments below.