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 on Mohs scale; Color: typically green (pale to dark), grayish, or mottled; Luster: waxy, greasy, or silky; Crystal Structure: Monoclinic; Cleavage: poor/irregular; Specific Gravity: 2.5–2.6.
- Hardness
- 3–6 on Mohs scale
- Color
- typically green (pale to dark), grayish, or mottled
- Luster
- waxy, greasy, or silky
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Physical properties
Hardness: 3–6 on Mohs scale; Color: typically green (pale to dark), grayish, or mottled; Luster: waxy, greasy, or silky; Crystal Structure: Monoclinic; Cleavage: poor/irregular; Specific Gravity: 2.5–2.6.
Formation & geological history
Formed through serpentinization, a low-temperature metamorphic process involving the hydration of ultramafic rocks (like peridotite) from the Earth's mantle, typically at tectonic plate boundaries/subduction zones.
Uses & applications
Used as decorative architectural stone, source of magnesium, historically for asbestos (in fibrous varieties), and in carvings/jewelry (often sold as 'New Jade').
Geological facts
It is the official state rock of California. When polished, it looks like snakeskin, hence the name. It often contains magnetite, making some specimens slightly magnetic.
Field identification & locations
Identify by its characteristic waxy 'soapy' feel and distinct green mottled appearance. Commonly found in ophiolitic belts such as the Coast Ranges of California, the Alps, and the Himalayas. Collectors should look for smooth, slickensided surfaces.
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