The metamorphic system can also react
differently if fluids are part of the system. Serpentinite, a mottled
green rock, is usually formed with high pressure and low temperature.
The original rock could contain a large amount of olivine (i.e.,
basalt). The olivine (Mg2SiO4) reacts with
water (H2O) to form the mineral serpentine (Mg3Si2O5(OH)4)plus
magnesium oxide (MgO).
Serpentinite is found in areas where faulting
occurs. Along the San Andreas fault zone in California, serpentinite is
so abundant it is recognized as the California state rock. The pressure
of shearing seems to be ideal for the serpentinite to form a
fibrous pattern. This form of serpentinite is a variety of asbestos,
which is used as a fire retardant.
Serpentinite with quartz veins