metamorphic
Serpentinite
Serpentinite (composed primarily of Serpentine group minerals, (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 lighter green or white mottling, Luster: Greasy, waxy, or silky, Crystal structure: Monoclinic, Cleavage: Usually poor or micaceous depending on variety, Specific Gravity: 2.5-3.2
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Physical properties
Hardness: 3-6 (Mohs scale), Color: Dark green to black with lighter green or white mottling, Luster: Greasy, waxy, or silky, Crystal structure: Monoclinic, Cleavage: Usually poor or micaceous depending on variety, Specific Gravity: 2.5-3.2
Formation & geological history
Formed through the hydration of ultramafic rocks (like peridotite) from the earth's mantle. This process, called serpentinization, typically occurs at tectonic plate boundaries where water interacts with mantle rocks under low temperature and high pressure.
Uses & applications
Used as an ornamental stone, for carvings, as a source of magnesium, and historically as an architectural facade. Industrial uses include heat-resistant materials and as a radiation shield in some nuclear reactors.
Geological facts
Serpentinite is the official state rock of California. It is unique because it often contains high levels of heavy metals like chromium and nickel, resulting in specialized 'serpentine soils' where only certain rare plants can grow.
Field identification & locations
Identify by its characteristic 'serpent-like' green mottled appearance, waxy feel, and common association with fault zones. Found frequently in the Coast Ranges of California and the Appalachian Mountains. Use a knife to check hardness; it is relatively soft and may show white streaks.
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