metamorphic
Serpentinite
Serpentinite (Mg, Fe, Ni, Al, Zn, Mn)2-3(Si, Al, Fe)2O5(OH)4
Hardness: 3-6 Mohs; Color: Dark green to black, mottled; Luster: Waxy, greasy, or silky; Crystal Structure: Monoclinic; Cleavage: Poor; Specific Gravity: 2.5-3.2
- Hardness
- 3-6 Mohs
- Color
- Dark green to black, mottled
- Luster
- Waxy, greasy, or silky
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Physical properties
Hardness: 3-6 Mohs; Color: Dark green to black, mottled; Luster: Waxy, greasy, or silky; Crystal Structure: Monoclinic; Cleavage: Poor; Specific Gravity: 2.5-3.2
Formation & geological history
Formed through the hydrothermal alteration of ultramafic rocks (like peridotite) from the Earth’s mantle at low temperatures, typically at tectonic plate boundaries/subduction zones.
Uses & applications
Used as decorative stone, construction material, a source of magnesium, and historically as a source of asbestos (though not all contain it). It is also a popular collector specimen.
Geological facts
Serpentinite is the official state rock of California. It is often called 'snake rock' because its texture and color resemble snakeskin. It forms in hydrated oceanic crust.
Field identification & locations
Identify by its characteristic waxy feel, green mottled appearance, and relatively soft surface. Commonly found in ophiolite complexes and along fault zones.
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