The serpentine group describes a group of common rock-forming hydrous magnesium iron phyllosilicate ((, )3) minerals, resulting from the metamorphism of the minerals that are contained in ultramafic rocks. They may contain minor amounts of other elements including chromium, manganese, cobalt or nickel. In mineralogy and gemology, 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.