metamorphic
Serpentine (Serpentinite)
Serpentinite (Mg, Fe, Ni, Al, Zn, Mn)2-3(Si, Al, Fe)2O5(OH)4
Hardness: 2.5–6 (variable); Color: Mottled green, dark green, or greenish-gray; Luster: Waxy, greasy, or silky; Crystal Structure: Monoclinic; Cleavage: Poor; Specific Gravity: 2.5–3.2.
- Hardness
- 2
- Color
- Mottled green, dark green, or greenish-gray
- Luster
- Waxy, greasy, or silky
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Physical properties
Hardness: 2.5–6 (variable); Color: Mottled green, dark green, or greenish-gray; 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, a process called serpentinization. This typically occurs at tectonic plate boundaries and subduction zones.
Uses & applications
Used as an ornamental stone for carvings, countertops, and decorative facades. High-grade translucent varieties (Nephrite-like) are used in jewelry. Historically used for asbestos production, though most modern uses avoid fibrous varieties.
Geological facts
Serpentinite is the official state rock of California. The name comes from its resemblance to the skin of a serpent. It often contains inclusions of magnetite, which can make the rock slightly magnetic.
Field identification & locations
Look for a distinct 'greasy' or 'soapy' feel to the touch and a mottled green color. It is commonly found in mountain ranges that were once ancient sea floors (ophiolites). Collectors should look for 'noble serpentine' which is translucent and bright green.
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