metamorphic
Serpentinite
Serpentinite (Mg, Fe, Ni, Al, Zn, Mn)3Si2O5(OH)4
Hardness: 2.5–6.0 (variable); Color: Deep green, yellowish-green, or brownish-green; Luster: Greasy, waxy, or silky; Crystal Structure: Monoclinic; Cleavage: Poor/none; Texture: Smooth or waxy to the touch.
- Hardness
- 2
- Color
- Deep green, yellowish-green, or brownish-green
- Luster
- Greasy, waxy, or silky
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Physical properties
Hardness: 2.5–6.0 (variable); Color: Deep green, yellowish-green, or brownish-green; Luster: Greasy, waxy, or silky; Crystal Structure: Monoclinic; Cleavage: Poor/none; Texture: Smooth or waxy to the touch.
Formation & geological history
Formed through serpentinization, a low-temperature metamorphic process where ultramafic rocks (like peridotite) from the Earth's mantle are hydrated by seawater or hydrothermal fluids, often at tectonic plate boundaries.
Uses & applications
Used as an ornamental stone in architecture, as a source for magnesium, historically for asbestos, and as jewelry (often called 'New Jade').
Geological facts
Serpentinite is the official state rock of California. It can contain small amounts of magnetite, making some specimens slightly magnetic. It often forms unique ecosystems called 'serpentine barrens' because of its high magnesium and low calcium content.
Field identification & locations
Identified by its distinctive 'serpentine' green color and waxy feel. Commonly found in ophiolite complexes, subduction zones, and mountain ranges like the Alps or the Coast Ranges of California. Look for 'slickensides' or shiny, polished surfaces caused by tectonic movement.
