The term asbestos refers to six naturally occurring fibrous minerals found in the veins of certain types of rocks. The six forms are chrysotile, amosite, crocidolite, anthophyllite, tremolite, and actinolite. The commonly used forms are chrysotile and amosite, known respectively as white and brown asbestos. Asbestos fibres, though microscopic, are incredibly durable, fire resistant and immune to most chemical attacks. These properties are the reasons that asbestos was commonly used in building materials.
Chrysotile asbestos is found within serpentine rocks and is made up of tiny needle like fibres. This is the most commonly used form of asbestos due to its high tensile strength and heat resistance. Chrysotile can also be spun into thread and woven into cloth.
The other five types of asbestos are found in amphibole rocks and are made up of softer, curlier fibres. They are also heat resistant but have a lower tensile strength and are unable to be spun or woven.