metamorphic
Serpentinite (often containing Jadeite/Nephrite)
Antigorite-rich Serpentine Rock, (Mg, Fe)3Si2O5(OH)4
Hardness: 3-6 (depending on mineral mix); Color: Mottled green, dark green, and white; Luster: Greasy, waxy, or silky; Crystal structure: Monoclinic; Cleavage: Poor; Specific gravity: 2.5–2.6.
- Hardness
- 3-6 (depending on mineral mix)
- Color
- Mottled green, dark green, and white
- Luster
- Greasy, waxy, or silky
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Physical properties
Hardness: 3-6 (depending on mineral mix); Color: Mottled green, dark green, and white; Luster: Greasy, waxy, or silky; Crystal structure: Monoclinic; Cleavage: Poor; 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 stone, in sculpture, as a source of magnesium, and sometimes as a low-grade gemstone (often marketed as 'New Jade'). Historically used for heat-resistant materials.
Geological facts
Serpentinite is the official state rock of California. It often contains inclusions of magnetite, which can make some specimens slightly magnetic.
Field identification & locations
Identify by its 'serpent-like' green mottled appearance and waxy feel. It is commonly found in ophiolite belts, such as those in the Coast Ranges of California, the Alps, and New Zealand.
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