metamorphic
Serpentinite
Serpentinite (composed primarily of serpentine group minerals like lizardite, chrysotile, or antigorite; Mg3Si2O5(OH)4)
Hardness: 3-6 Mohs (varies by composition); Color: Mottled green, dark green, or blackish-green; Luster: Greasy, waxy, or silky; Crystal structure: Monoclinic; Cleavage: Poor; Specific gravity: 2.5-3.2.
- Hardness
- 3-6 Mohs (varies by composition)
- Color
- Mottled green, dark green, or blackish-green
- Luster
- Greasy, waxy, or silky
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Physical properties
Hardness: 3-6 Mohs (varies by composition); Color: Mottled green, dark green, or blackish-green; Luster: Greasy, waxy, or silky; Crystal structure: Monoclinic; Cleavage: Poor; Specific gravity: 2.5-3.2.
Formation & geological history
Formed through the hydrothermal metamorphism (serpentinization) of mafic and ultramafic igneous rocks (like peridotite) from the Earth's mantle, typically at tectonic plate boundaries or seafloor spreading centers.
Uses & applications
Used primarily as decorative stone, in construction as 'Verde Antique' marble, as a source for magnesium, and historically as a source for asbestos (though this carries health risks). Large, high-quality pieces are used for sculpture.
Geological facts
Serpentinite is the state rock of California. It is unique because it contains high concentrations of heavy metals like nickel and chromium while being low in essential nutrients, leading to the evolution of specific 'serpentine-endemic' plant species.
Field identification & locations
Identify in the field by its characteristic 'serpentine' green color, greasy feel, and often 'slickensided' shiny surfaces created by tectonic movement. Found in mountain belts like the Appalachians, the Alps, and the Coast Ranges of California.
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