metamorphic
Serpentine / Serpentinite (with Weathering Crust)
Serpentinite (Mg,Fe,Ni,Al,Zn,Mn)2-3(Si,Al,Fe)2O5(OH)4
Hardness: 3-6 on Mohs scale. Color: Greenish-grey interior with a distinct brown-orange iron oxide weathering rind. Luster: Waxy, greasy, or dull. Crystal Structure: Monoclinic/Orthorhombic (microcrystalline). Cleavage: Poor to uneven fracture. Specific Gravity: 2.5-2.6.
- Hardness
- 3-6 on Mohs scale
- Luster
- Waxy, greasy, or dull
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Physical properties
Hardness: 3-6 on Mohs scale. Color: Greenish-grey interior with a distinct brown-orange iron oxide weathering rind. Luster: Waxy, greasy, or dull. Crystal Structure: Monoclinic/Orthorhombic (microcrystalline). Cleavage: Poor to uneven fracture. Specific Gravity: 2.5-2.6.
Formation & geological history
Formed via serpentinization, a low-temperature metamorphic process where mafic and ultramafic rocks (like peridotite from the Earth's mantle) are hydrated and altered by water at subduction zones and mid-ocean ridges.
Uses & applications
Used historically as decorative stone, carving material, source of asbestos (chrysotile), industrial source of magnesium, and as road ballast or aggregate.
Geological facts
Serpentinite is the state rock of California. The dark exterior rim on this specimen is a classic weathering crust (rind) formed by iron oxidation during subaerial exposure.
Field identification & locations
Can be identified in the field by its distinct greenish core contrast with the yellowish-brown iron-stained outer crust, greasy to slippery feel when smooth, and moderate hardness. Commonly found in ophiolite complexes, mountain belts, and subduction zones worldwide.
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