Serpentinized

Serpentinized refers to rocks or minerals that have undergone serpentinization, a low‑temperature, water‑rich alteration of ultramafic rocks such as peridotite, dunite, and harzburgite. During serpentinization olivine and pyroxene react with circulating fluids to form serpentine group minerals (lizardite, chrysotile, antigorite). The reaction commonly yields secondary minerals such as magnetite, brucite, talc, and various carbonates, and it often releases hydrogen gas.

The process occurs at shallow crustal levels where ultramafic rocks interact with water, typically under low to moderate temperatures (roughly 50 to 400°C) and various pressures. It is especially prevalent at mid‑ocean ridges, in ophiolites, and in subduction‑zone complexes where mantle rocks are exposed to fluids during tectonic deformation. Serpentinization can facilitate hydrothermal circulation and alter the physical properties of rock, producing highly fractured, cohesive, greenish to brownish serpentinite bodies.

Serpentinite rocks tend to be relatively weak and ductile at shallow depths, with lower density compared with their protoliths, influencing faulting behavior and seismic responses. The serpentine minerals retain water in their structure, contributing to high fluid contents and altered rheology. Serpentinized terrains are also notable for supporting unique subsurface microbial ecosystems that couple hydrogen and carbon compounds produced during alteration.

Economically and geopolitically, serpentinites can host magnetite and accessory metals, and certain serpentine deposits have been associated with chrysotile asbestos in historical contexts. However, chrysotile presents significant health hazards, and modern assessments emphasize caution in handling such materials.