Serpentine is a group of common rock-forming hydrous magnesium iron phyllosilicate ((Mg, Fe) 3Si2O5 (OH) 4) minerals; it may contain minor amounts of other elements including chromium, manganese, cobalt and nickel. In mineralogy and gemmology, serpentine may refer to any of 20 varieties belonging to the serpentine group. Owing to admixture, these varieties are not always easy to individualize, and distinctions are not usually made. There are three important mineral polymorphs of serpentine: antigorite, chrysotile and lizardite.