metamorphic
Serpentinite
Serpentinite (composed largely of Serpentine group minerals like Antigorite, Lizardite, and Chrysotile: Mg3Si2O5(OH)4)
Hardness: 3-6 (Mohs), Color: Dark green to black with mottled light green/white patches, Luster: Greasy, waxy, or dull; often appears shiny when wet, Crystal structure: Usually massive or fibrous, Cleavage: Poor to perfect depending on mineral variety, Specific gravity: 2.5-3.2
- Luster
- Greasy, waxy, or dull
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Physical properties
Hardness: 3-6 (Mohs), Color: Dark green to black with mottled light green/white patches, Luster: Greasy, waxy, or dull; often appears shiny when wet, Crystal structure: Usually massive or fibrous, Cleavage: Poor to perfect depending on mineral variety, Specific gravity: 2.5-3.2
Formation & geological history
Formed through serpentinization, a low-temperature metamorphic process where ultra-mafic rocks from the Earth's mantle (like peridotite) are hydrated by seawater or hydrothermal fluids at tectonic plate boundaries.
Uses & applications
Used as decorative stone, in sculpture, as a source of asbestos (historically), and as industrial ballast or aggregate. Some varieties are used in jewelry as 'New Jade'.
Geological facts
Serpentinite is the official State Rock of California. It is often associated with the 'greenstone belts' and is a key indicator of ancient seafloor subduction zones.
Field identification & locations
Identify by its characteristic 'snake-skin' mottled green appearance and waxy feel. It is commonly found in ophiolite complexes, such as those in the Coast Ranges of California, the Appalachians, and the Alps.
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