metamorphic
Serpentinite
Serpentinite (Mg, Fe, Ni, Al, Zn, Mn)2-3(Si, Al, Fe)2O5(OH)4
Hardness: 3-6 (Mohs scale), Color: Dark green to black with mottled oily patches, Luster: Greasy, waxy or silky, Crystal Structure: Monoclinic (fibrous or platy), Specific Gravity: 2.2-2.9
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Physical properties
Hardness: 3-6 (Mohs scale), Color: Dark green to black with mottled oily patches, Luster: Greasy, waxy or silky, Crystal Structure: Monoclinic (fibrous or platy), Specific Gravity: 2.2-2.9
Formation & geological history
Formed by the low-temperature hydrothermal metamorphic alteration of ultramafic rocks (like peridotite) from the Earth's mantle, a process known as serpentinization, typically at tectonic plate boundaries.
Uses & applications
Used as a decorative architectural stone, source of asbestos (historically), carving material for sculpture, and sometimes as a source of magnesium or nickel.
Geological facts
Serpentinite is the official state rock of California; it is often associated with rare plants that can tolerate its high magnesium and heavy metal content.
Field identification & locations
Identified in the field by its distinctive green color, soapy or waxy feel, and common occurrence in ophiolite complexes; look for slickensided surfaces (shiny, polished faces).
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