serpentinize

Serpentinize is a geological process in which ultramafic rocks, especially olivine- and pyroxene-rich rocks such as peridotite and dunite, react with circulating water or fluids to form serpentine minerals. The serpentine group includes chrysotile, lizardite, and antigorite. Along with serpentine, the reaction often yields secondary minerals such as brucite and magnetite, and can liberate molecular hydrogen.

The process occurs at relatively low temperatures and shallow to moderate pressures, in settings where fluids can permeate fractured rock. It is characteristic of hydrothermal systems at mid-ocean ridges, in ophiolites exposed in subduction zones, and in mantle wedges undergoing hydration. Serpentinization can proceed over short to long timescales, from thousands to millions of years, and is typically exothermic in its early stages. Water-rock interaction under these conditions modifies mineralogy, texture, and porosity.

Geochemical and geophysical consequences are significant. The reaction transforms primary minerals into serpentine and associated phases, often reducing rock density and altering mechanical properties. It enhances permeability and fracture development, facilitating fluid circulation. Hydrogen gas is commonly produced, providing energy sources for certain microorganisms and influencing deep biosphere chemistry. Serpentinization also consumes water and promotes carbonate formation, contributing to long-term carbon cycling. Some serpentine minerals, notably chrysotile, have been used historically as asbestos, a practice now restricted due to health risks. In planetary science, serpentinization is of interest as a potential source of hydrogen and methane in icy and rocky bodies.