How is Asbestos Formed?

Jul 24, 2020

One common misconception that we hear from clients is that asbestos can grow in a property. While some environmental contaminants such as mold or bacteria can grow within a property, asbestos can not. The term asbestos refers to a group of minerals that are inorganic and naturally occurring. In this blog, we will discuss how is asbestos formed. WARNING: some serious geology terms lie ahead!

Mineral Formation

Asbestos minerals were used in manufacturing due to their numerous benefits. These benefits include fireproofing, durability, sound absorption, chemical resistance, and many others. Asbestos is collected by mining sources out of the ground where the minerals are present. Asbestos has been mined since antiquity, and has been recorded in the works of the Greek philosopher Pliny. Asbestos, along with other minerals, form under specific conditions that are dictated by the local geology and environmental conditions. The process of mineral formation begins with a solution. This solution can be created from magma, liquids within the source rock, or changes due to pressure or thermal changes. Once the solution cools, the atoms within arrange themselves into a crystal framework, also known as a crystal lattice. Thus, the mineral is formed.


The most common form of asbestos is called chrysotile. Out of the two mineral groups of asbestos — serpentine or amphibole — chrysotile is the only member of the serpentine group. The formation of chrysotile begins with the process of serpentinization within a source rock. Serpentinization occurs typically when water creates a solution within ultramafic (low-silica,high-iron) igneous rock or metaphorically altered limestone deposits.The result of serpinitizination leads to the creation of serpentine minerals or serpentinite, which is a rock formed of typically more than one serpentine mineral variety. The hydrothermal alteration that occurs can precipitate chyrostile. Chrysotile mines can be found in various areas throughout the world, but American manufacturers often used chrysotile mined from Canada in their products.


Amosite is the most common amphibole variety of asbestos found in building materials. Amosite is not a mineralogical term but actually refers to the company Amosa which mined it. Amosa stands for Asbestos Mined out of South Africa. The source material that forms amosite is a magnesium rich amphibole mineral called cummingtonite-grunerite — what a mouthful! Through hydrothermal alteration, amosite is formed similarly to chrysotile. Amosite can also be found in Europe and New Zealand.  Anthophyllite, an even rarer asbestos mineral, is actually a polymorph of cummingtonite-grunerite. A polymorph is a material that has the same chemical composition, but a different crystal structure. 

Crocidolite is the second most common amphibole asbestos mineral found in materials. It is actually the hydrothermally formed fibrous variety of the mineral Riebeckite. Riebeckite is a blue mineral that is a sodium-rich amphibole. It can be found in South Africa, Australia, and Bolivia. Tremolite and Actinolite are formed similarly to chrysotile and are from certain igneous rocks or altered limestone from metamorphic processes. These minerals form a solid solution in which one will form depending on the concentration of iron or magnesium present in the source rock. Tremolite is more magnesium-rich, while actinolite is richer in iron. Tremolite can be found as a contaminant in chrysotile, talc, and vermiculite deposits. 


In conclusion, asbestos does not grow in the traditional sense such as organic environmental contaminants like mold or bacteria. These minerals are formed under complex geological processes, which are mined and placed in building materials for various purposes. To find out where to find asbestos at a property, reference this previous blog.