Serpentine subgroup  The serpentine subgroup (part of the kaolinite-serpentine group) are greenish, brownish, or spotted minerals commonly found in serpentinite rocks. They are used as a source of magnesium and asbestos, and as a decorative stone. The name is thought to come from the greenish color being that of a serpent. 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. The serpentine group of minerals are polymorphous, meaning that they have the same chemical formulae, but the atoms are arranged into different structures, or crystal lattices. Chrysotile, which has a fiberous habit, is one polymorph of serpentine and is one of the more important asbestos minerals. Other polymorphs in the serpentine group may have a platy habit. Antigorite and lizardite are the polymorphs with platy habit. Many types of serpentine have been used for jewellery and hardstone carving, sometimes under the name "false jade" or "Teton jade". Their olive green colour and smooth or scaly appearance is the basis of the name from the Latin "serpentinus", meaning "serpent rock," according to Best (2003). They have their origins in metamorphic alterations of peridotite and pyroxene. Serpentines may also pseudomorphously replace other magnesium silicates. Alterations may be incomplete, causing physical properties of serpentines to vary widely. Where they form a significant part of the land surface, the soil is unusually high in clay. Antigorite is the polymorph of serpentine that most commonly forms during metamorphism of wet ultramafic rocks and is stable at the highest temperatures—to over at depths of or so. In contrast, lizardite and chrysotile typically form near the Earth's surface and break down at relatively low temperatures, probably well below . It has been suggested that chrysotile is never stable relative to either of the other two serpentine polymorphs.