metamorphic
Serpentinite
Serpentinite (Mg, Fe, Ni, Al, Zn, Mn)2-3(Si, Al, Fe)2O5(OH)4
Hardness: 3-6 (Mohs scale), Color: Dull to mottled green, yellowish-green to black, Luster: Waxy to greasy, Crystal structure: Monoclinic (fine-grained), Cleavage: Varies, Specific gravity: 2.2-2.9
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Physical properties
Hardness: 3-6 (Mohs scale), Color: Dull to mottled green, yellowish-green to black, Luster: Waxy to greasy, Crystal structure: Monoclinic (fine-grained), Cleavage: Varies, Specific gravity: 2.2-2.9
Formation & geological history
Formed by the hydration of ultramafic rocks (like peridotite) from the Earth’s mantle at low temperatures. Common in Alpine-type mountain belts like the Western Alps where the user is located.
Uses & applications
Historically used for decorative stone facades and sculptures (e.g., 'Verde Alpi'). Small, pretty river stones are popular among collectors.
Geological facts
Serpentinite is the state rock of California but is exceptionally common in the Piedmont region of Italy. It is a major component of ophiolites, which are sections of oceanic crust uplifted onto land.
Field identification & locations
Identified by its distinctive smooth, waxy feel and green mottling. Abundantly found as river-worn pebbles in the Stura di Demonte and other rivers draining the Cottian and Maritime Alps.
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