metamorphic
Serpentinite
Serpentinite (Mg, Fe, Ni, Al, Zn, Mn)2-3(Si, Al, Fe)2O5(OH)4
Hardness: 3-6 (variable), Color: Waxy shades of green with dark speckles (magnetite/chromite), Luster: Greasy or waxy, Crystal structure: Monoclinic, Cleavage: Poor, Specific Gravity: 2.2-2.9
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Physical properties
Hardness: 3-6 (variable), Color: Waxy shades of green with dark speckles (magnetite/chromite), Luster: Greasy or waxy, Crystal structure: Monoclinic, Cleavage: Poor, Specific Gravity: 2.2-2.9
Formation & geological history
Formed through serpentinization, the low-temperature metamorphic alteration of ultramafic rocks (peridotite) from the Earth's mantle by hydrothermal fluids at tectonic plate boundaries.
Uses & applications
Used for architectural cladding, decorative stone (California State Rock), as a source of magnesium, and limited use in carvings/jewelry.
Geological facts
Serpentinite is the state rock of California. It often creates unique, nutrient-poor soils that support rare endemic plant species that can tolerate high heavy metal concentrations.
Field identification & locations
Identify by its 'slickensides' (polished surfaces) and distinctive greasy feel. Commonly found in ophiolite complexes, the Coast Ranges, and the Appalachian Mountains. Use a magnet to check for dark magnetite grains.
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