There is no single chemical formula for asbestos, as it refers to a group of naturally occurring fibrous minerals that belong to the serpentine or amphibole group of minerals. The chemical composition and formula of asbestos can vary depending on the specific mineral type.

Two common types of asbestos are:

- Chrysotile: The chemical formula for chrysotile asbestos is Mg3Si2O5(OH)4. It is a serpentine mineral composed of magnesium, silicon, and oxygen.

- Amosite: The chemical formula for amosite asbestos is (Fe,Mg)7Si8O22(OH)2. It is an amphibole mineral composed of varying amounts of iron, magnesium, silicon, and oxygen.

Other types of asbestos include crocidolite, tremolite, actinolite, and anthophyllite, each with its own distinct chemical formula.