Serpentinization

Serpentinization is a hydration and metamorphic transformation of ferromagnesian minerals, such as olivine and pyroxene, in mafic and ultramafic rock to produce serpentinite. The minerals it forms include the serpentine group minerals antigorite, lizardite and chrysotile, along with brucite, talc, nickel-iron alloys and magnetite. It is a low-temperature form of metamorphism driven largely by hydration and oxidation, in which water is the oxidizing agent and is itself reduced to hydrogen. The rock absorbs large amounts of water, so its density falls from about 3.3 to 2.5 grams per cubic centimetre and its volume grows by roughly 30 to 40 percent. The reaction releases heat, providing an energy source for non-volcanic hydrothermal vents, and the alteration is particularly important at the sea floor at tectonic plate boundaries.