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