metamorphic
Greenstone / Serpentinite
Serpentinite (composed largely of Serpentine group minerals, Mg3Si2O5(OH)4)
Hardness: 3-6 (variable), Color: Waxy dull to dark green, Luster: Greasy to silky, Crystal structure: Monoclinic, Cleavage: Poor, Specific gravity: 2.2-2.9
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Physical properties
Hardness: 3-6 (variable), Color: Waxy dull to dark green, Luster: Greasy to silky, Crystal structure: Monoclinic, Cleavage: Poor, Specific gravity: 2.2-2.9
Formation & geological history
Formed through serpentinization, a process where ultramafic rocks (like peridotite) from the Earth's mantle are hydrated and chemically transformed by low-temperature metamorphic fluids at tectonic plate boundaries.
Uses & applications
Used as decorative stone in architecture, as a source for magnesium and asbestos (historically), and sometimes carved for jewelry or ornaments.
Geological facts
Serpentinite is the official state rock of California. It often forms in subduction zones and is frequently associated with unusual soil chemistry that supports rare endemic plant species.
Field identification & locations
Identified by its distinctive greenish hue, smooth waxy feel, and common association with oceanic crustal sequences (ophiolites). Found in mountain ranges like the Alps, Appalachians, and the California Coast Ranges.
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