Serpentinite

Serpentinite is a metamorphic rock composed mainly of serpentine-group minerals. It forms when water chemically alters ultramafic rocks, especially peridotite.

Serpentinization: The hydration and chemical alteration of ultramafic rocks that produces serpentine minerals and related phases. This process transforms peridotite into the rock and mineral assemblages that define serpentinite.
Ultramafic rock: An igneous rock with very low silica content and abundant magnesium- and iron-rich minerals. Serpentinite forms by altering ultramafic rocks, a broader class that includes its common precursors.
Ophiolite: A fragment of oceanic lithosphere and upper mantle exposed on land. Serpentinite commonly occurs within ophiolites, preserving evidence of oceanic mantle alteration.
Lost City Hydrothermal Field: A seafloor hydrothermal system on the Mid-Atlantic Ridge where alkaline fluids emerge from serpentinized rocks. Its vents demonstrate active serpentinization and hydrogen-rich fluid production.
Peridotite: A coarse-grained ultramafic igneous rock composed chiefly of olivine and pyroxene. It is the common parent rock whose hydration produces serpentinite.
Mantle rock: Rock derived from Earth's mantle, typically rich in magnesium and iron. Much serpentinite originates from mantle material exposed to circulating water.
Asbestos: A group of fibrous silicate minerals whose inhaled fibers can cause serious disease. Some serpentinites contain chrysotile, an asbestos mineral requiring careful assessment during excavation.
Zermatt-Saas ophiolite: An Alpine ophiolite containing rocks from former oceanic lithosphere, including serpentinites. Its serpentinites preserve evidence of ocean-floor alteration and later subduction.
Olivine: A magnesium-iron silicate mineral common in Earth's mantle and in ultramafic rocks. Hydration of olivine is a central reaction during serpentinization.
Tectonic plate: A large, rigid section of Earth's lithosphere that moves over the underlying asthenosphere. Plate boundaries expose mantle rocks and provide pathways for seawater to enter them.

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