metamorphic
Serpentinite
Serpentinite (Mg3Si2O5(OH)4)
Hardness: 3-6 Mohs. Color: Green, grayish-green, or brownish. Luster: Waxy to greasy. Crystal structure: Monoclinic (fibrous or platy). Cleavage: Poor. Specific gravity: 2.2-2.9.
- Hardness
- 3-6 Mohs
- Color
- Green, grayish-green, or brownish
- Luster
- Waxy to greasy
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Physical properties
Hardness: 3-6 Mohs. Color: Green, grayish-green, or brownish. Luster: Waxy to greasy. Crystal structure: Monoclinic (fibrous or platy). Cleavage: Poor. Specific gravity: 2.2-2.9.
Formation & geological history
Formed through the hydrothermal alteration (serpentinization) of ultramafic rocks like peridotite from the Earth's mantle, typically at tectonic plate boundaries/subduction zones.
Uses & applications
Used as a decorative stone in architecture, as a source of magnesium, and historically as a precursor for asbestos. High-quality varieties are used for carvings and jewelry.
Geological facts
Serpentinite is the official state rock of California. It can contain rare minerals like magnetite and chromite, and its presence often creates unique 'serpentine soils' that support rare endemic plants.
Field identification & locations
Identify by its characteristic 'serpent-like' green color, greasy feel, and smooth, polished 'slickenside' surfaces. Common in mountain belts where oceanic crust has been uplifted.
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