metamorphic
Serpentine (Nephrite-like River Cobble)
Serpentinite (Hydrous Magnesium Iron Silicate)
Hardness: 3-6 (depending on mineral mix); Color: Olive to dark green with black mottling; Luster: Waxy to greasy when wet; Structure: Microcrystalline/Massive; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8
- Hardness
- 3-6 (depending on mineral mix)
- Color
- Olive to dark green with black mottling
- Luster
- Waxy to greasy when wet
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Physical properties
Hardness: 3-6 (depending on mineral mix); Color: Olive to dark green with black mottling; Luster: Waxy to greasy when wet; Structure: Microcrystalline/Massive; Cleavage: None (conchoidal fracture); Specific Gravity: 2.5-2.8
Formation & geological history
Formed through serpentinization, where ultramafic rocks from the Earth's mantle are chemically altered by low-temperature hydrothermal fluids, often at tectonic plate boundaries/subduction zones.
Uses & applications
Used as decorative stone, carvings, bookends, and occasionally as a lower-cost substitute for jade (Nephrite). Large deposits are mined for industrial magnesium and once for asbestos.
Geological facts
Serpentinite is the official state rock of California. It often creates 'serpentine barrens' where the soil is toxic to most plants but supports rare, endemic flora.
Field identification & locations
Identify in the field by its soapy or greasy feel, characteristic green color, and its presence in riverbeds near mountain ranges. It is often softer than a steel knife, unlike true Jadeite.
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