Chrysotile or white asbestos is a soft, fibrous silicate mineral in the serpentine group of phyllosilicates: as such, it is distinct from other asbestiform minerals in the amphibole group. Its idealized chemical formula is Mg3(Si2O5)(OH)4, in which some of the magnesium ions may be replaced by iron or other cations. Substitution of the hydroxide ions for fluoride, oxide or chloride is also known, but rarer.
A related, but much rarer, mineral is Népouite, in which all the magnesium cations of chrysotile are substituted by nickel cations.
Three polytypes of chrysotile are known. These are very difficult to distinguish in hand specimens, and polarized light microscopy must normally be used. Some older publications refer to chrysotile as a group of minerals.