metamorphic
Greenstone / Serpentinite
Serpentinite (Mg, Fe, Ni, Al, Zn, Mn)2-3(Si, Al, Fe)2O5(OH)4
Hardness: 3-6 (variable); Color: Dark green to light yellowish-green with mottled or veined patterns; Luster: Greasy, waxy, or silky; Crystal structure: Monoclinic (usually massive/fibrous); Specific gravity: 2.2-2.9.
- Hardness
- 3-6 (variable)
- Luster
- Greasy, waxy, or silky
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Physical properties
Hardness: 3-6 (variable); Color: Dark green to light yellowish-green with mottled or veined patterns; Luster: Greasy, waxy, or silky; Crystal structure: Monoclinic (usually massive/fibrous); Specific gravity: 2.2-2.9.
Formation & geological history
Formed through serpentinization, a low-temperature metamorphic process where ultramafic rocks from the Earth's mantle are hydrated at tectonic plate boundaries (subduction zones). Likely Paleozoic to Mesozoic in age.
Uses & applications
Used as an ornamental stone (sculptures, architectural cladding), a source of magnesium, and historically as a source of asbestos. High-quality varieties like 'Bowenite' are used in jewelry.
Geological facts
Serpentinite is the official state rock of California. It is unique because it often supports specialized flora (serpentine barrens) that can tolerate high heavy metal concentrations and low calcium.
Field identification & locations
Identify in the field by its distinct 'snake-skin' appearance, soapy feel, and green hue. Common in ophiolite complexes, the Coast Ranges of California, and the Appalachian Mountains. Use a scratch test to differentiate from harder nephrite jade.
