metamorphic
Serpentinite
Serpentinite (composed mainly of Serpentine-group minerals: (Mg, Fe)3Si2O5(OH)4)
Hardness: 3-6 (variable), Color: dark green to black with mottled patches, Luster: waxy or greasy to silky, Structure: massive or fibrous, Cleavage: poor, Specific Gravity: 2.2-2.9.
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Physical properties
Hardness: 3-6 (variable), Color: dark green to black with mottled patches, Luster: waxy or greasy to silky, Structure: massive or fibrous, Cleavage: poor, Specific Gravity: 2.2-2.9.
Formation & geological history
Forms through the hydrothermal metamorphism (serpentinization) of mafic and ultramafic rocks like peridotite from the Earth's mantle; typically occurs at tectonic plate boundaries and subduction zones.
Uses & applications
Used as a decorative architectural stone (verde antique), as source material for asbestos (historically), in jewelry as a jade look-alike, and as a shield against radiation in nuclear reactors.
Geological facts
Serpentinite is the official state rock of California. It can contain toxic elements like mercury and chromium, and the soils it produces are often low in nutrients, leading to unique ecosystems of rare plants.
Field identification & locations
Identify by its characteristic 'snake-skin' appearance, soapy feel, and green color. Common in ophiolite complexes and mountain belts like the Appalachians, Alps, and Coast Ranges.
