metamorphic
Serpentinite
Serpentinite (composed primarily of mineral group (Mg, Fe, Ni, Al, Zn, Mn)2-3(Si, Al, Fe)2O5(OH)4)
Hardness: 3-6 (Mohs scale), Color: various shades of green, grayish-green, to nearly black, Luster: greasy, waxy, or silky, Crystal structure: Monoclinic, Cleavage: poor (often fractures in splinters), Specific gravity: 2.2–2.9
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Physical properties
Hardness: 3-6 (Mohs scale), Color: various shades of green, grayish-green, to nearly black, Luster: greasy, waxy, or silky, Crystal structure: Monoclinic, Cleavage: poor (often fractures in splinters), Specific gravity: 2.2–2.9
Formation & geological history
Formed through serpentinization, a low-temperature metamorphic process where ultramafic rocks (like peridotite) from the Earth's mantle/oceanic lithosphere are hydrated by seawater near subduction zones or mid-ocean ridges.
Uses & applications
Used as an architectural ornamental stone (verde antique), as a source of magnesium, historically used for asbestos, and as shielding in nuclear reactors due to its water content.
Geological facts
Serpentinite is the state rock of California. It is often associated with rare plants because its soil lacks essential nutrients like calcium while containing heavy metals. It is often 'slickensided' (polished) due to tectonic movement.
Field identification & locations
Identify in the field by its distinctive 'serpent-like' green mottled color and waxy feel. Commonly found in ophiolite complexes, such as the Coast Ranges of California, the Alps, and the Appalachian Mountains. Collectors look for translucent 'noble serpentine' varieties.
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