metamorphic
Serpentinite
Serpentinite (Mg, Fe, Ni, Al, Zn, Mn)2-3(Si, Al, Fe)2O5(OH)4
Hardness: 3-6 Mohs. Color: Greenish, blackish-green, or brownish-yellow. Luster: Greasy, waxy, or silky. Crystal structure: Fibrous or platy (as minerals like chrysotile or lizardite). Cleavage: Poorly defined. Specific Gravity: 2.5-3.3.
- Hardness
- 3-6 Mohs
- Color
- Greenish, blackish-green, or brownish-yellow
- Luster
- Greasy, waxy, or silky
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Physical properties
Hardness: 3-6 Mohs. Color: Greenish, blackish-green, or brownish-yellow. Luster: Greasy, waxy, or silky. Crystal structure: Fibrous or platy (as minerals like chrysotile or lizardite). Cleavage: Poorly defined. Specific Gravity: 2.5-3.3.
Formation & geological history
Formed through the process of serpentinization, which involves the hydrothermal alteration of ultramafic rocks (like peridotite) from the Earth's mantle at low temperatures. Common at tectonic plate boundaries.
Uses & applications
Used as an ornamental stone in architecture, as a source of asbestos (historically), in jewelry (lapidary), and as a ballast for railways.
Geological facts
Serpentinite is the official state rock of California. It can contain rare minerals and is often associated with high concentrations of heavy metals like chromium and nickel.
Field identification & locations
Look for a distinctive 'serpent-like' green mottled color and a slick, greasy feel (slickensides). It is common in mountainous regions like the Coastal Ranges or the Alps. Handle with care if fibrous, as it may contain asbestos minerals.
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