metamorphic
Greenstone / Serpentinite
Serpentinite (Mg, Fe, Ni, Al, Zn, Mn)3(Si, Al, Fe)2O5(OH)4
Hardness: 2.5 to 5 on Mohs scale; Color: Sage green to dark forest green with mottled patterns; Luster: Waxy to greasy; Crystal Structure: Monoclinic; Cleavage: Poor/fractured; Texture: Fine-grained and dense.
- Hardness
- 2
- Color
- Sage green to dark forest green with mottled patterns
- Luster
- Waxy to greasy
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Physical properties
Hardness: 2.5 to 5 on Mohs scale; Color: Sage green to dark forest green with mottled patterns; Luster: Waxy to greasy; Crystal Structure: Monoclinic; Cleavage: Poor/fractured; Texture: Fine-grained and dense.
Formation & geological history
Formed through serpentinization, a low-temperature metamorphic process where ultramafic rocks from the Earth's mantle are hydrated and chemically transformed by seawater or hydrothermal fluids, often at tectonic plate boundaries.
Uses & applications
Used historically for carvings, jewelry (as 'New Zealand Jade' or Bowenite), decorative building facades, and as a source of magnesium. It is common in lapidary work and garden landscaping.
Geological facts
Serpentinite is the official state rock of California. It often contains veins of chrysotile (asbestos), though in solid rock form it is generally safe to handle. It often creates unique soil chemistry that supports rare plant life.
Field identification & locations
Identify by its distinct green color, waxy feel, and relatively low hardness (often scratchable with a copper penny or steel knife). Look for it in ophiolite complexes and along major fault zones. Collectors should look for chatoyancy or high-translucency varieties.
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