Asbestos refers to 6 different minerals with very similar attributes. Asbestos has 2 sub-categories. They are Asbestos-Amphibole and Asbestos-Serpentine. They are categorized as such, due to the way in which they form. Serpentines form when certain igneous rocks come in contact with just-below-boiling water. A chemical reaction takes place creating a Serpentine rock. There is only one serpentine rock: Chrysotile. Amphibole rocks are generally dark, inosilicate minerals, composed of a double-chain SiO4 tetrahedron. Their chemical compositions are similar to pyroxene.