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), Color: Waxy green to blackish-green, Luster: Greasy or waxy to silky, Crystal Structure: Monoclinic/Orthorhombic (microcrystalline), Cleavage: Poor, Specific Gravity: 2.5-3.3
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Physical properties
Hardness: 3-6 (Mohs), Color: Waxy green to blackish-green, Luster: Greasy or waxy to silky, Crystal Structure: Monoclinic/Orthorhombic (microcrystalline), Cleavage: Poor, Specific Gravity: 2.5-3.3
Formation & geological history
Formed through the hydration of ultramafic rocks (like peridotite) from the Earth's mantle at low temperatures. Common in subduction zones and oceanic crust.
Uses & applications
Used as decorative stone, sculpture medium (soapstone varieties), a source of magnesium, and historically as fire-resistant insulation (when containing asbestos fibers).
Geological facts
Serpentinite is the official state rock of California. It is often called 'serpentine,' which is actually the group of minerals that make up the rock.
Field identification & locations
Identify in the field by its waxy 'snake-skin' appearance, soapy feel, and green color. Often found in mountain ranges that were once ancient seafloors, such as the Coast Ranges or the Alps.
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